How come it says array is undefined?

How come it says array is undefined? - javascript

Here is a javascript sample:
var obj =
{
options: [],
init: function( )
{
options['one'] = 'one';
for( k in options )
{
alert( options[k] );
}
}
};
instead of prompting "one", it says undefined, why?

You would need to reference it as obj.options.
Aside from that, you should use an object {} instead of an array [] if you're not going to be using numeric indexes.
var obj =
{
options: {},
init: function( )
{
obj.options['one'] = 'one';
for( k in obj.options )
{
alert( obj.options[k] );
}
}
};
If you call the init() function from the obj reference, then you could use this inside the init function instead of obj.
var obj =
{
options: {},
init: function( )
{
this.options['one'] = 'one';
for( k in this.options )
{
alert( this.options[k] );
}
}
};
obj.init(); // Makes `this` refer to `obj` in the `init` function
As #CMS noted, you should declare your variables with var. In your for loop, k is no declared with var, and as such will become a global variable.

What you're doing looks very similar, in form and concept, to something called the 'Module pattern' in javascript.
It is a very powerful tool, and if you want to learn I highly recommend you read up on it.
Here is your code, rewritten as a module, with changes to avoid polluting the global scope, and to fix a potential problem with your for in loop.
It also defines options as an object, rather than an array, as you seem to be using it as a hashtable rather than with numeric indices.
var module = (function() {
//here options is private
var options = {};
var init = function() {
options['one'] = 'one';
for (var k in options) {
if(options.hasOwnProperty(k)){
alert(options[k]);
}
}
};
//These are the things that are public
return {
init:init
};
}());
module.init();
alert(module.options); //undefined (because it's private)

Related

How can I detect when an Object is getting called in JavaScript

How do I detect when a JavaScript object is being accessed? I mean like a scope object, not a global object or a property of a object. I would like to be able to do something like this:
"use strict"
!function() {
var o = {
onaccess: function() {
console.log("o was accessed");
}
}
var x = o; //"o was accessed" when this happens.
}();

You can't that way as you are not accessing an object, but the reference to that object.
What you can try to do is to create a getter in the "global scope" (AKA window in browsers, for example) or to create an object with getters as properties, which you can think of "variables in objects".
(function() {
var _x = {};
Object.defineProperty(window, 'x', {
get: function() {
alert("access");
return _x;
}
});
document.getElementById("g").addEventListener("click", function() {
var a = x;
});
document.getElementById("w").addEventListener("click", function() {
var a = window.x;
});
})();
<button id="g">Access global x</button>
<button id="w">Access window x</button>
This code works because when you acces a variable (x in this case), it will run through the upper scopes until it finds an scope which contains the variable. It will finally look for the variable in the global scope, which is window, where I've set a getter that will run each time window.x is called (or simply x, which will end in accessing window.x internally).
This is hacky and I don't recomment it as you have to define a global variable. You can however try to create an object with getters in some properties (the same way as window.x), so you don't have to work with the global scope, but this way you have to always access the object property by prepending the object:
(function() {
var _x = {};
var prop = {};
Object.defineProperty(prop, 'x', {
get: function() {
alert("access");
return _x;
}
});
document.getElementById("w").addEventListener("click", function() {
var a = prop.x;
});
})();
<button id="w">Access property x</button>
Note that this will only work with predefined variable names. If you want to capture "all" variables, you can work with Proxies, which are impossible to hack over the global scope (window) but will work with objects, like this:
var h = {
get: function(target, name){
alert("Accessed property " + name);
}
};
var p = new Proxy({}, h);
document.getElementById("x").addEventListener("click", function() {
var a = p.x;
});
document.getElementById("y").addEventListener("click", function() {
var a = p.y;
});
document.getElementById("r").addEventListener("click", function() {
var a = p[Math.random()];
});
<button id="x">Access x property</button>
<button id="y">Access y property</button>
<button id="r">Access random property</button>

You can make a proxy, then you can log something everytime your function is called, be careful though Proxies are not 100% polyfillable in IE11 or less
function realFunction() {
return {
a: "5"
}
}
var proxy = new Proxy(realFunction, {
get: function(target, key) {
const obj = target();
console.log("key", `'${key}'`, "was called on", target);
return obj[key];
}
});
proxy.a // "5"

Call a function from a variable [duplicate]

I have the name of a function in JavaScript as a string. How do I convert that into a function pointer so I can call it later?
Depending on the circumstances, I may need to pass various arguments into the method too.
Some of the functions may take the form of namespace.namespace.function(args[...]).

Don't use eval unless you absolutely, positively have no other choice.
As has been mentioned, using something like this would be the best way to do it:
window["functionName"](arguments);
That, however, will not work with a namespace'd function:
window["My.Namespace.functionName"](arguments); // fail
This is how you would do that:
window["My"]["Namespace"]["functionName"](arguments); // succeeds
In order to make that easier and provide some flexibility, here is a convenience function:
function executeFunctionByName(functionName, context /*, args */) {
var args = Array.prototype.slice.call(arguments, 2);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for(var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
return context[func].apply(context, args);
}
You would call it like so:
executeFunctionByName("My.Namespace.functionName", window, arguments);
Note, you can pass in whatever context you want, so this would do the same as above:
executeFunctionByName("Namespace.functionName", My, arguments);

Just thought I'd post a slightly altered version of Jason Bunting's very helpful function.
First, I have simplified the first statement by supplying a second parameter to slice(). The original version was working fine in all browsers except IE.
Second, I have replaced this with context in the return statement; otherwise, this was always pointing to window when the target function was being executed.
function executeFunctionByName(functionName, context /*, args */) {
var args = Array.prototype.slice.call(arguments, 2);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for (var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
return context[func].apply(context, args);
}

The answer to this other question shows you how to do that: Javascript equivalent of Python's locals()?
Basically, you can say
window["foo"](arg1, arg2);
or as many others have suggested, you can just use eval:
eval(fname)(arg1, arg2);
although this is extremely unsafe unless you're absolutely sure about what you're eval-ing.

I think an elegant way of doing this is by defining your functions in a hash object. Then you can have a reference to those functions from the hash using the string. e.g.
var customObject = {
customFunction: function(param){...}
};
Then you can call:
customObject['customFunction'](param);
Where customFunction will be a string matching a function defined in your object.
UPDATE
It seems that this answer was helpful for many fellow coders out there so here goes an updated version.
With ES6 you can additionally use Computed Property Names which will allow you to avoid magic strings.
const FunctionNames = Object.freeze({
FirstFunction: "firstFunction",
SecondFunction: "secondFunction"
});
...
var customObject = {
[FunctionNames.FirstFunction]: function(param){...},
[FunctionNames.SecondFunction]: function(param){...}
};
...
customObject[FunctionNames.FirstFunction](param);

Could you not just do this:
var codeToExecute = "My.Namespace.functionName()";
var tmpFunc = new Function(codeToExecute);
tmpFunc();
You can also execute any other JavaScript using this method.

With ES6 you could to access class methods by name:
class X {
method1(){
console.log("1");
}
method2(){
this['method1']();
console.log("2");
}
}
let x = new X();
x['method2']();
the output would be:
1
2

Two things:
avoid eval, it's terribly dangerous and slow
secondly it doesn't matter where your function exists, "global" -ness is irrelevant. x.y.foo() can be enabled through x.y['foo']() or x['y']['foo']() or even window['x']['y']['foo'](). You can chain indefinitely like this.

All the answers assume that the functions can be accessed through global scope (window). However, the OP did not make this assumption.
If the functions live in a local scope (aka closure) and are not referenced by some other local object, bad luck: You have to use eval() AFAIK, see
dynamically call local function in javascript

Depending on where you are you can also use:
this["funcname"]();
self["funcname"]();
window["funcname"]();
top["funcname"]();
globalThis["funcname"]();
or, in nodejs
global["funcname"]()

Here is my contribution to Jason Bunting's / Alex Nazarov's excellent answers, where I include error checking requested by Crashalot.
Given this (contrived) preamble:
a = function( args ) {
console.log( 'global func passed:' );
for( var i = 0; i < arguments.length; i++ ) {
console.log( '-> ' + arguments[ i ] );
}
};
ns = {};
ns.a = function( args ) {
console.log( 'namespace func passed:' );
for( var i = 0; i < arguments.length; i++ ) {
console.log( '-> ' + arguments[ i ] );
}
};
name = 'nsa';
n_s_a = [ 'Snowden' ];
noSuchAgency = function(){};
then the following function:
function executeFunctionByName( functionName, context /*, args */ ) {
var args, namespaces, func;
if( typeof functionName === 'undefined' ) { throw 'function name not specified'; }
if( typeof eval( functionName ) !== 'function' ) { throw functionName + ' is not a function'; }
if( typeof context !== 'undefined' ) {
if( typeof context === 'object' && context instanceof Array === false ) {
if( typeof context[ functionName ] !== 'function' ) {
throw context + '.' + functionName + ' is not a function';
}
args = Array.prototype.slice.call( arguments, 2 );
} else {
args = Array.prototype.slice.call( arguments, 1 );
context = window;
}
} else {
context = window;
}
namespaces = functionName.split( "." );
func = namespaces.pop();
for( var i = 0; i < namespaces.length; i++ ) {
context = context[ namespaces[ i ] ];
}
return context[ func ].apply( context, args );
}
will allow you to call a javascript function by name stored in a string, either namespaced or global, with or without arguments (including Array objects), providing feedback on any errors encountered (hopefully catching them).
The sample output shows how it works:
// calling a global function without parms
executeFunctionByName( 'a' );
/* OUTPUT:
global func passed:
*/
// calling a global function passing a number (with implicit window context)
executeFunctionByName( 'a', 123 );
/* OUTPUT:
global func passed:
-> 123
*/
// calling a namespaced function without parms
executeFunctionByName( 'ns.a' );
/* OUTPUT:
namespace func passed:
*/
// calling a namespaced function passing a string literal
executeFunctionByName( 'ns.a', 'No Such Agency!' );
/* OUTPUT:
namespace func passed:
-> No Such Agency!
*/
// calling a namespaced function, with explicit context as separate arg, passing a string literal and array
executeFunctionByName( 'a', ns, 'No Such Agency!', [ 007, 'is the man' ] );
/* OUTPUT:
namespace func passed:
-> No Such Agency!
-> 7,is the man
*/
// calling a global function passing a string variable (with implicit window context)
executeFunctionByName( 'a', name );
/* OUTPUT:
global func passed:
-> nsa
*/
// calling a non-existing function via string literal
executeFunctionByName( 'n_s_a' );
/* OUTPUT:
Uncaught n_s_a is not a function
*/
// calling a non-existing function by string variable
executeFunctionByName( n_s_a );
/* OUTPUT:
Uncaught Snowden is not a function
*/
// calling an existing function with the wrong namespace reference
executeFunctionByName( 'a', {} );
/* OUTPUT:
Uncaught [object Object].a is not a function
*/
// calling no function
executeFunctionByName();
/* OUTPUT:
Uncaught function name not specified
*/
// calling by empty string
executeFunctionByName( '' );
/* OUTPUT:
Uncaught is not a function
*/
// calling an existing global function with a namespace reference
executeFunctionByName( 'noSuchAgency', ns );
/* OUTPUT:
Uncaught [object Object].noSuchAgency is not a function
*/

You just need convert your string to a pointer by window[<method name>].
example:
var function_name = "string";
function_name = window[function_name];
and now you can use it like a pointer.

Here is my Es6 approach which enables you to call your function by it's name as string or it's function name and also enable you to pass different numbers of arguments to different types of functions:
function fnCall(fn, ...args)
{
let func = (typeof fn =="string")?window[fn]:fn;
if (typeof func == "function") func(...args);
else throw new Error(`${fn} is Not a function!`);
}
function example1(arg1){console.log(arg1)}
function example2(arg1, arg2){console.log(arg1 + " and " + arg2)}
function example3(){console.log("No arguments!")}
fnCall("example1", "test_1");
fnCall("example2", "test_2", "test3");
fnCall(example3);
fnCall("example4"); // should raise an error in console

If you want to call a function of an object instead of a global function with window["functionName"]. You can do it like;
var myObject=new Object();
myObject["functionName"](arguments);
Example:
var now=new Date();
now["getFullYear"]()

BE CAREFUL!!!
One should try to avoid calling a function by string in JavaScript for two reasons:
Reason 1: Some code obfuscators will wreck your code as they will change the function names, making the string invalid.
Reason 2: It is much harder to maintain code that uses this methodology as it is much harder to locate usages of the methods called by a string.

Surprised to see no mention of setTimeout.
To run a function without arguments:
var functionWithoutArguments = function(){
console.log("Executing functionWithoutArguments");
}
setTimeout("functionWithoutArguments()", 0);
To run function with arguments:
var functionWithArguments = function(arg1, arg2) {
console.log("Executing functionWithArguments", arg1, arg2);
}
setTimeout("functionWithArguments(10, 20)");
To run deeply namespaced function:
var _very = {
_deeply: {
_defined: {
_function: function(num1, num2) {
console.log("Execution _very _deeply _defined _function : ", num1, num2);
}
}
}
}
setTimeout("_very._deeply._defined._function(40,50)", 0);

I don't think you need complicated intermediate functions or eval or be dependent on global variables like window:
function fun1(arg) {
console.log(arg);
}
function fun2(arg) {
console.log(arg);
}
const operations = {
fun1,
fun2
};
operations["fun1"]("Hello World");
operations.fun2("Hello World");
// You can use intermediate variables, if you like
let temp = "fun1";
operations[temp]("Hello World");
It will also work with imported functions:
// mode.js
export function fun1(arg) {
console.log(arg);
}
export function fun2(arg) {
console.log(arg);
}
// index.js
import { fun1, fun2 } from "./mod";
const operations = {
fun1,
fun2
};
operations["fun1"]("Hello World");
operations["fun2"]("Hello World");
Since it is using property access, it will survive minimization or obfuscation, contrary to some answers you will find here.

So, like others said, definitely the best option is:
window['myfunction'](arguments)
And like Jason Bunting said, it won't work if the name of your function includes an object:
window['myobject.myfunction'](arguments); // won't work
window['myobject']['myfunction'](arguments); // will work
So here's my version of a function that will execute all functions by name (including an object or not):
my = {
code : {
is : {
nice : function(a, b){ alert(a + "," + b); }
}
}
};
guy = function(){ alert('awesome'); }
function executeFunctionByName(str, args)
{
var arr = str.split('.');
var fn = window[ arr[0] ];
for (var i = 1; i < arr.length; i++)
{ fn = fn[ arr[i] ]; }
fn.apply(window, args);
}
executeFunctionByName('my.code.is.nice', ['arg1', 'arg2']);
executeFunctionByName('guy');

let t0 = () => { alert('red0') }
var t1 = () =>{ alert('red1') }
var t2 = () =>{ alert('red2') }
var t3 = () =>{ alert('red3') }
var t4 = () =>{ alert('red4') }
var t5 = () =>{ alert('red5') }
var t6 = () =>{ alert('red6') }
function getSelection(type) {
var evalSelection = {
'title0': t0,
'title1': t1,
'title2': t2,
'title3': t3,
'title4': t4,
'title5': t5,
'title6': t6,
'default': function() {
return 'Default';
}
};
return (evalSelection[type] || evalSelection['default'])();
}
getSelection('title1');
A more OOP solution ...

One more detail on Jason and Alex's posts. I found it helpful to add a default value to context. Just put context = context == undefined? window:context; at the beginning of the function. You can change window to whatever your preferred context is, and then you won't need to pass in the same variable each time you call this in your default context.

To add to Jason Bunting's answer, if you're using nodejs or something (and this works in dom js, too), you could use this instead of window (and remember: eval is evil:
this['fun'+'ctionName']();

There's a very similar thing in my code.
I have a server-generated string which contains a function name which I need to pass as a callback for a 3rd party library. So I have a code that takes the string and returns a "pointer" to the function, or null if it isn't found.
My solution was very similar to "Jason Bunting's very helpful function" *, although it doesn't auto-execute, and the context is always on the window. But this can be easily modified.
Hopefully this will be helpful to someone.
/**
* Converts a string containing a function or object method name to a function pointer.
* #param string func
* #return function
*/
function getFuncFromString(func) {
// if already a function, return
if (typeof func === 'function') return func;
// if string, try to find function or method of object (of "obj.func" format)
if (typeof func === 'string') {
if (!func.length) return null;
var target = window;
var func = func.split('.');
while (func.length) {
var ns = func.shift();
if (typeof target[ns] === 'undefined') return null;
target = target[ns];
}
if (typeof target === 'function') return target;
}
// return null if could not parse
return null;
}

Here's a bit robust and reusable solution I ended up implementing for one of my projects.
A FunctionExecutor Constructor Function
Usage:
let executor = new FunctionExecutor();
executor.addFunction(two)
executor.addFunction(three)
executor.execute("one");
executor.execute("three");
Obviously in the project the adding of all the functions that required to be called by name was done by a loop.
The function Executor:
function FunctionExecutor() {
this.functions = {};
this.addFunction = function (fn) {
let fnName = fn.name;
this.functions[fnName] = fn;
}
this.execute = function execute(fnName, ...args) {
if (fnName in this.functions && typeof this.functions[fnName] === "function") {
return this.functions[fnName](...args);
}
else {
console.log("could not find " + fnName + " function");
}
}
this.logFunctions = function () {
console.log(this.functions);
}
}
Example Usage:
function two() {
console.log("two");
}
function three() {
console.log("three");
}
let executor = new FunctionExecutor();
executor.addFunction(two)
executor.addFunction(three)
executor.execute("one");
executor.execute("three");

There too some very helpful way.
http://devlicio.us/blogs/sergio_pereira/archive/2009/02/09/javascript-5-ways-to-call-a-function.aspx
var arrayMaker = {
someProperty: 'some value here',
make: function (arg1, arg2) {
return [ this, arg1, arg2 ];
},
execute: function_name
};

I can't resist mentioning another trick, which helps if you have an unknown number of arguments that are also being passed as part of the string containing the function name. For example:
var annoyingstring = 'call_my_func(123, true, "blah")';
If your Javascript is running on a HTML page, all you need is an invisible link; you can pass a string into the onclick attribute, and the call the click method.
<!-- invisible -->
$('#link_secret').attr('onclick', annoyingstring);
$('#link_secret').click();
Or create the <a> element at runtime.

Easiest way is to access it like has element
window.ClientSideValidations.forms.location_form
is same as
window.ClientSideValidations.forms['location_form']

People keep saying that eval is dangerous and evil because it can run any arbitrary code. However, if you use eval with a whitelisting approach, assuming you know all the possible function names that may need to be run in advance, then eval is no longer a security concern because the input is no longer arbitrary. Whitelisting is a good and frequent security pattern. Here's an example:
function runDynamicFn(fnName, ...args) {
// can also be fed from a tightly controlled config
const allowedFnNames = ['fn1', 'ns1.ns2.fn3', 'ns4.fn4'];
return allowedFnNames.includes(fnName) ? eval(fnName)(...args) : undefined;
}
// test function:
function fn1(a) {
console.log('fn1 called with', a)
}
runDynamicFn('alert("got you!")')
runDynamicFn('fn1', 'foo')

Look basic:
var namefunction = 'jspure'; // String
function jspure(msg1 = '', msg2 = '') {
console.log(msg1+(msg2!=''?'/'+msg2:''));
} // multiple argument
// Results ur test
window[namefunction]('hello','hello again'); // something...
eval[namefunction] = 'hello'; // use string or something, but its eval just one argument and not exist multiple
Exist other type function is class and look example nils petersohn

Thanks for the very helpful answer. I'm using Jason Bunting's function in my projects.
I extended it to use it with an optional timeout, because the normal way to set a timeout wont work. See abhishekisnot's question
function executeFunctionByName(functionName, context, timeout /*, args */ ) {
var args = Array.prototype.slice.call(arguments, 3);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for (var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
var timeoutID = setTimeout(
function(){ context[func].apply(context, args)},
timeout
);
return timeoutID;
}
var _very = {
_deeply: {
_defined: {
_function: function(num1, num2) {
console.log("Execution _very _deeply _defined _function : ", num1, num2);
}
}
}
}
console.log('now wait')
executeFunctionByName("_very._deeply._defined._function", window, 2000, 40, 50 );

There are several executeByName functions here which works fine, unless name contains square brackets - issue I ran into - as I have dynamically generated names. So above functions will fail on names like
app.widget['872LfCHc']['toggleFolders']
As a remedy, I've made function to take this into account too, maybe someone will find it usefull:
Generated from CoffeeScript:
var executeByName = function(name, context) {
var args, func, i, j, k, len, len1, n, normalizedName, ns;
if (context == null) {
context = window;
}
args = Array.prototype.slice.call(arguments, 2);
normalizedName = name.replace(/[\]'"]/g, '').replace(/\[/g, '.');
ns = normalizedName.split(".");
func = context;
for (i = j = 0, len = ns.length; j < len; i = ++j) {
n = ns[i];
func = func[n];
}
ns.pop();
for (i = k = 0, len1 = ns.length; k < len1; i = ++k) {
n = ns[i];
context = context[n];
}
if (typeof func !== 'function') {
throw new TypeError('Cannot execute function ' + name);
}
return func.apply(context, args);
}
For better readability check also CoffeeScript version:
executeByName = (name, context = window) ->
args = Array.prototype.slice.call(arguments, 2)
normalizedName = name.replace(/[\]'"]/g, '').replace(/\[/g, '.')
ns = normalizedName.split "."
func = context
for n, i in ns
func = func[n]
ns.pop()
for n, i in ns
context = context[n];
if typeof func != 'function'
throw new TypeError 'Cannot execute function ' + name
func.apply(context, args)

You can call javascript function within the eval("functionname as string") either. Like below: (eval is pure javascript function)
function testfunc(){
return "hello world";
}
$( document ).ready(function() {
$("div").html(eval("testfunc"));
});
Working example: https://jsfiddle.net/suatatan/24ms0fna/4/

Why can't I reference an object literal from inside an object literal?

not sure if this is possible or if I'm doing it wrong. I'm trying to have an object literal reference one of it's own properties that is another object literal. I keep getting an error stating that it is undefined:
var MyObject = {
init: function(){
this.elements.buttons.click(function(){
alert('hit');
});
},
elements: {
buttons: $('button')
}
}
what am i doing wrong?
UPDATE:
main.js is calling init to initialize on demand which probably doofed the scope --
function executeFunctionByName(functionName, context /*, args */) {
var args = [].slice.call(arguments).splice(2);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for(var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
return context[func].apply(this, args);
}
$(document).ready(function(){
// invoke init() for any element that requests it
$('[data-page]').each(function(i, p){
var page = 'APP.MODEL.' + $(p).data('page') + '.init';
executeFunctionByName(page, window)
});
});

If you are invoking that function directly without going through MyObject, this would be undefined. Replace this with MyObject and it should work.
This would not work as this would be defined to window:
var MyObject = {
// init: ...
}
var init = MyObject.init;
init();
See 3. Entering function code: How does the "this" keyword work?
If you wish to continue to use this, you may use Function.prototype.call() or Function.prototype.apply() like so:
var MyObject = {
// init: ...
}
var init = MyObject.init;
init.call(MyObject);

Is it possible to use a function parameter as part of a jquery statement [duplicate]

I have the name of a function in JavaScript as a string. How do I convert that into a function pointer so I can call it later?
Depending on the circumstances, I may need to pass various arguments into the method too.
Some of the functions may take the form of namespace.namespace.function(args[...]).

Don't use eval unless you absolutely, positively have no other choice.
As has been mentioned, using something like this would be the best way to do it:
window["functionName"](arguments);
That, however, will not work with a namespace'd function:
window["My.Namespace.functionName"](arguments); // fail
This is how you would do that:
window["My"]["Namespace"]["functionName"](arguments); // succeeds
In order to make that easier and provide some flexibility, here is a convenience function:
function executeFunctionByName(functionName, context /*, args */) {
var args = Array.prototype.slice.call(arguments, 2);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for(var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
return context[func].apply(context, args);
}
You would call it like so:
executeFunctionByName("My.Namespace.functionName", window, arguments);
Note, you can pass in whatever context you want, so this would do the same as above:
executeFunctionByName("Namespace.functionName", My, arguments);

Just thought I'd post a slightly altered version of Jason Bunting's very helpful function.
First, I have simplified the first statement by supplying a second parameter to slice(). The original version was working fine in all browsers except IE.
Second, I have replaced this with context in the return statement; otherwise, this was always pointing to window when the target function was being executed.
function executeFunctionByName(functionName, context /*, args */) {
var args = Array.prototype.slice.call(arguments, 2);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for (var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
return context[func].apply(context, args);
}

The answer to this other question shows you how to do that: Javascript equivalent of Python's locals()?
Basically, you can say
window["foo"](arg1, arg2);
or as many others have suggested, you can just use eval:
eval(fname)(arg1, arg2);
although this is extremely unsafe unless you're absolutely sure about what you're eval-ing.

I think an elegant way of doing this is by defining your functions in a hash object. Then you can have a reference to those functions from the hash using the string. e.g.
var customObject = {
customFunction: function(param){...}
};
Then you can call:
customObject['customFunction'](param);
Where customFunction will be a string matching a function defined in your object.
UPDATE
It seems that this answer was helpful for many fellow coders out there so here goes an updated version.
With ES6 you can additionally use Computed Property Names which will allow you to avoid magic strings.
const FunctionNames = Object.freeze({
FirstFunction: "firstFunction",
SecondFunction: "secondFunction"
});
...
var customObject = {
[FunctionNames.FirstFunction]: function(param){...},
[FunctionNames.SecondFunction]: function(param){...}
};
...
customObject[FunctionNames.FirstFunction](param);

Could you not just do this:
var codeToExecute = "My.Namespace.functionName()";
var tmpFunc = new Function(codeToExecute);
tmpFunc();
You can also execute any other JavaScript using this method.

With ES6 you could to access class methods by name:
class X {
method1(){
console.log("1");
}
method2(){
this['method1']();
console.log("2");
}
}
let x = new X();
x['method2']();
the output would be:
1
2

Two things:
avoid eval, it's terribly dangerous and slow
secondly it doesn't matter where your function exists, "global" -ness is irrelevant. x.y.foo() can be enabled through x.y['foo']() or x['y']['foo']() or even window['x']['y']['foo'](). You can chain indefinitely like this.

All the answers assume that the functions can be accessed through global scope (window). However, the OP did not make this assumption.
If the functions live in a local scope (aka closure) and are not referenced by some other local object, bad luck: You have to use eval() AFAIK, see
dynamically call local function in javascript

Depending on where you are you can also use:
this["funcname"]();
self["funcname"]();
window["funcname"]();
top["funcname"]();
globalThis["funcname"]();
or, in nodejs
global["funcname"]()

Here is my contribution to Jason Bunting's / Alex Nazarov's excellent answers, where I include error checking requested by Crashalot.
Given this (contrived) preamble:
a = function( args ) {
console.log( 'global func passed:' );
for( var i = 0; i < arguments.length; i++ ) {
console.log( '-> ' + arguments[ i ] );
}
};
ns = {};
ns.a = function( args ) {
console.log( 'namespace func passed:' );
for( var i = 0; i < arguments.length; i++ ) {
console.log( '-> ' + arguments[ i ] );
}
};
name = 'nsa';
n_s_a = [ 'Snowden' ];
noSuchAgency = function(){};
then the following function:
function executeFunctionByName( functionName, context /*, args */ ) {
var args, namespaces, func;
if( typeof functionName === 'undefined' ) { throw 'function name not specified'; }
if( typeof eval( functionName ) !== 'function' ) { throw functionName + ' is not a function'; }
if( typeof context !== 'undefined' ) {
if( typeof context === 'object' && context instanceof Array === false ) {
if( typeof context[ functionName ] !== 'function' ) {
throw context + '.' + functionName + ' is not a function';
}
args = Array.prototype.slice.call( arguments, 2 );
} else {
args = Array.prototype.slice.call( arguments, 1 );
context = window;
}
} else {
context = window;
}
namespaces = functionName.split( "." );
func = namespaces.pop();
for( var i = 0; i < namespaces.length; i++ ) {
context = context[ namespaces[ i ] ];
}
return context[ func ].apply( context, args );
}
will allow you to call a javascript function by name stored in a string, either namespaced or global, with or without arguments (including Array objects), providing feedback on any errors encountered (hopefully catching them).
The sample output shows how it works:
// calling a global function without parms
executeFunctionByName( 'a' );
/* OUTPUT:
global func passed:
*/
// calling a global function passing a number (with implicit window context)
executeFunctionByName( 'a', 123 );
/* OUTPUT:
global func passed:
-> 123
*/
// calling a namespaced function without parms
executeFunctionByName( 'ns.a' );
/* OUTPUT:
namespace func passed:
*/
// calling a namespaced function passing a string literal
executeFunctionByName( 'ns.a', 'No Such Agency!' );
/* OUTPUT:
namespace func passed:
-> No Such Agency!
*/
// calling a namespaced function, with explicit context as separate arg, passing a string literal and array
executeFunctionByName( 'a', ns, 'No Such Agency!', [ 007, 'is the man' ] );
/* OUTPUT:
namespace func passed:
-> No Such Agency!
-> 7,is the man
*/
// calling a global function passing a string variable (with implicit window context)
executeFunctionByName( 'a', name );
/* OUTPUT:
global func passed:
-> nsa
*/
// calling a non-existing function via string literal
executeFunctionByName( 'n_s_a' );
/* OUTPUT:
Uncaught n_s_a is not a function
*/
// calling a non-existing function by string variable
executeFunctionByName( n_s_a );
/* OUTPUT:
Uncaught Snowden is not a function
*/
// calling an existing function with the wrong namespace reference
executeFunctionByName( 'a', {} );
/* OUTPUT:
Uncaught [object Object].a is not a function
*/
// calling no function
executeFunctionByName();
/* OUTPUT:
Uncaught function name not specified
*/
// calling by empty string
executeFunctionByName( '' );
/* OUTPUT:
Uncaught is not a function
*/
// calling an existing global function with a namespace reference
executeFunctionByName( 'noSuchAgency', ns );
/* OUTPUT:
Uncaught [object Object].noSuchAgency is not a function
*/

You just need convert your string to a pointer by window[<method name>].
example:
var function_name = "string";
function_name = window[function_name];
and now you can use it like a pointer.

Here is my Es6 approach which enables you to call your function by it's name as string or it's function name and also enable you to pass different numbers of arguments to different types of functions:
function fnCall(fn, ...args)
{
let func = (typeof fn =="string")?window[fn]:fn;
if (typeof func == "function") func(...args);
else throw new Error(`${fn} is Not a function!`);
}
function example1(arg1){console.log(arg1)}
function example2(arg1, arg2){console.log(arg1 + " and " + arg2)}
function example3(){console.log("No arguments!")}
fnCall("example1", "test_1");
fnCall("example2", "test_2", "test3");
fnCall(example3);
fnCall("example4"); // should raise an error in console

If you want to call a function of an object instead of a global function with window["functionName"]. You can do it like;
var myObject=new Object();
myObject["functionName"](arguments);
Example:
var now=new Date();
now["getFullYear"]()

BE CAREFUL!!!
One should try to avoid calling a function by string in JavaScript for two reasons:
Reason 1: Some code obfuscators will wreck your code as they will change the function names, making the string invalid.
Reason 2: It is much harder to maintain code that uses this methodology as it is much harder to locate usages of the methods called by a string.

Surprised to see no mention of setTimeout.
To run a function without arguments:
var functionWithoutArguments = function(){
console.log("Executing functionWithoutArguments");
}
setTimeout("functionWithoutArguments()", 0);
To run function with arguments:
var functionWithArguments = function(arg1, arg2) {
console.log("Executing functionWithArguments", arg1, arg2);
}
setTimeout("functionWithArguments(10, 20)");
To run deeply namespaced function:
var _very = {
_deeply: {
_defined: {
_function: function(num1, num2) {
console.log("Execution _very _deeply _defined _function : ", num1, num2);
}
}
}
}
setTimeout("_very._deeply._defined._function(40,50)", 0);

I don't think you need complicated intermediate functions or eval or be dependent on global variables like window:
function fun1(arg) {
console.log(arg);
}
function fun2(arg) {
console.log(arg);
}
const operations = {
fun1,
fun2
};
operations["fun1"]("Hello World");
operations.fun2("Hello World");
// You can use intermediate variables, if you like
let temp = "fun1";
operations[temp]("Hello World");
It will also work with imported functions:
// mode.js
export function fun1(arg) {
console.log(arg);
}
export function fun2(arg) {
console.log(arg);
}
// index.js
import { fun1, fun2 } from "./mod";
const operations = {
fun1,
fun2
};
operations["fun1"]("Hello World");
operations["fun2"]("Hello World");
Since it is using property access, it will survive minimization or obfuscation, contrary to some answers you will find here.

So, like others said, definitely the best option is:
window['myfunction'](arguments)
And like Jason Bunting said, it won't work if the name of your function includes an object:
window['myobject.myfunction'](arguments); // won't work
window['myobject']['myfunction'](arguments); // will work
So here's my version of a function that will execute all functions by name (including an object or not):
my = {
code : {
is : {
nice : function(a, b){ alert(a + "," + b); }
}
}
};
guy = function(){ alert('awesome'); }
function executeFunctionByName(str, args)
{
var arr = str.split('.');
var fn = window[ arr[0] ];
for (var i = 1; i < arr.length; i++)
{ fn = fn[ arr[i] ]; }
fn.apply(window, args);
}
executeFunctionByName('my.code.is.nice', ['arg1', 'arg2']);
executeFunctionByName('guy');

let t0 = () => { alert('red0') }
var t1 = () =>{ alert('red1') }
var t2 = () =>{ alert('red2') }
var t3 = () =>{ alert('red3') }
var t4 = () =>{ alert('red4') }
var t5 = () =>{ alert('red5') }
var t6 = () =>{ alert('red6') }
function getSelection(type) {
var evalSelection = {
'title0': t0,
'title1': t1,
'title2': t2,
'title3': t3,
'title4': t4,
'title5': t5,
'title6': t6,
'default': function() {
return 'Default';
}
};
return (evalSelection[type] || evalSelection['default'])();
}
getSelection('title1');
A more OOP solution ...

One more detail on Jason and Alex's posts. I found it helpful to add a default value to context. Just put context = context == undefined? window:context; at the beginning of the function. You can change window to whatever your preferred context is, and then you won't need to pass in the same variable each time you call this in your default context.

To add to Jason Bunting's answer, if you're using nodejs or something (and this works in dom js, too), you could use this instead of window (and remember: eval is evil:
this['fun'+'ctionName']();

There's a very similar thing in my code.
I have a server-generated string which contains a function name which I need to pass as a callback for a 3rd party library. So I have a code that takes the string and returns a "pointer" to the function, or null if it isn't found.
My solution was very similar to "Jason Bunting's very helpful function" *, although it doesn't auto-execute, and the context is always on the window. But this can be easily modified.
Hopefully this will be helpful to someone.
/**
* Converts a string containing a function or object method name to a function pointer.
* #param string func
* #return function
*/
function getFuncFromString(func) {
// if already a function, return
if (typeof func === 'function') return func;
// if string, try to find function or method of object (of "obj.func" format)
if (typeof func === 'string') {
if (!func.length) return null;
var target = window;
var func = func.split('.');
while (func.length) {
var ns = func.shift();
if (typeof target[ns] === 'undefined') return null;
target = target[ns];
}
if (typeof target === 'function') return target;
}
// return null if could not parse
return null;
}

Here's a bit robust and reusable solution I ended up implementing for one of my projects.
A FunctionExecutor Constructor Function
Usage:
let executor = new FunctionExecutor();
executor.addFunction(two)
executor.addFunction(three)
executor.execute("one");
executor.execute("three");
Obviously in the project the adding of all the functions that required to be called by name was done by a loop.
The function Executor:
function FunctionExecutor() {
this.functions = {};
this.addFunction = function (fn) {
let fnName = fn.name;
this.functions[fnName] = fn;
}
this.execute = function execute(fnName, ...args) {
if (fnName in this.functions && typeof this.functions[fnName] === "function") {
return this.functions[fnName](...args);
}
else {
console.log("could not find " + fnName + " function");
}
}
this.logFunctions = function () {
console.log(this.functions);
}
}
Example Usage:
function two() {
console.log("two");
}
function three() {
console.log("three");
}
let executor = new FunctionExecutor();
executor.addFunction(two)
executor.addFunction(three)
executor.execute("one");
executor.execute("three");

There too some very helpful way.
http://devlicio.us/blogs/sergio_pereira/archive/2009/02/09/javascript-5-ways-to-call-a-function.aspx
var arrayMaker = {
someProperty: 'some value here',
make: function (arg1, arg2) {
return [ this, arg1, arg2 ];
},
execute: function_name
};

I can't resist mentioning another trick, which helps if you have an unknown number of arguments that are also being passed as part of the string containing the function name. For example:
var annoyingstring = 'call_my_func(123, true, "blah")';
If your Javascript is running on a HTML page, all you need is an invisible link; you can pass a string into the onclick attribute, and the call the click method.
<!-- invisible -->
$('#link_secret').attr('onclick', annoyingstring);
$('#link_secret').click();
Or create the <a> element at runtime.

Easiest way is to access it like has element
window.ClientSideValidations.forms.location_form
is same as
window.ClientSideValidations.forms['location_form']

People keep saying that eval is dangerous and evil because it can run any arbitrary code. However, if you use eval with a whitelisting approach, assuming you know all the possible function names that may need to be run in advance, then eval is no longer a security concern because the input is no longer arbitrary. Whitelisting is a good and frequent security pattern. Here's an example:
function runDynamicFn(fnName, ...args) {
// can also be fed from a tightly controlled config
const allowedFnNames = ['fn1', 'ns1.ns2.fn3', 'ns4.fn4'];
return allowedFnNames.includes(fnName) ? eval(fnName)(...args) : undefined;
}
// test function:
function fn1(a) {
console.log('fn1 called with', a)
}
runDynamicFn('alert("got you!")')
runDynamicFn('fn1', 'foo')

Look basic:
var namefunction = 'jspure'; // String
function jspure(msg1 = '', msg2 = '') {
console.log(msg1+(msg2!=''?'/'+msg2:''));
} // multiple argument
// Results ur test
window[namefunction]('hello','hello again'); // something...
eval[namefunction] = 'hello'; // use string or something, but its eval just one argument and not exist multiple
Exist other type function is class and look example nils petersohn

Thanks for the very helpful answer. I'm using Jason Bunting's function in my projects.
I extended it to use it with an optional timeout, because the normal way to set a timeout wont work. See abhishekisnot's question
function executeFunctionByName(functionName, context, timeout /*, args */ ) {
var args = Array.prototype.slice.call(arguments, 3);
var namespaces = functionName.split(".");
var func = namespaces.pop();
for (var i = 0; i < namespaces.length; i++) {
context = context[namespaces[i]];
}
var timeoutID = setTimeout(
function(){ context[func].apply(context, args)},
timeout
);
return timeoutID;
}
var _very = {
_deeply: {
_defined: {
_function: function(num1, num2) {
console.log("Execution _very _deeply _defined _function : ", num1, num2);
}
}
}
}
console.log('now wait')
executeFunctionByName("_very._deeply._defined._function", window, 2000, 40, 50 );

There are several executeByName functions here which works fine, unless name contains square brackets - issue I ran into - as I have dynamically generated names. So above functions will fail on names like
app.widget['872LfCHc']['toggleFolders']
As a remedy, I've made function to take this into account too, maybe someone will find it usefull:
Generated from CoffeeScript:
var executeByName = function(name, context) {
var args, func, i, j, k, len, len1, n, normalizedName, ns;
if (context == null) {
context = window;
}
args = Array.prototype.slice.call(arguments, 2);
normalizedName = name.replace(/[\]'"]/g, '').replace(/\[/g, '.');
ns = normalizedName.split(".");
func = context;
for (i = j = 0, len = ns.length; j < len; i = ++j) {
n = ns[i];
func = func[n];
}
ns.pop();
for (i = k = 0, len1 = ns.length; k < len1; i = ++k) {
n = ns[i];
context = context[n];
}
if (typeof func !== 'function') {
throw new TypeError('Cannot execute function ' + name);
}
return func.apply(context, args);
}
For better readability check also CoffeeScript version:
executeByName = (name, context = window) ->
args = Array.prototype.slice.call(arguments, 2)
normalizedName = name.replace(/[\]'"]/g, '').replace(/\[/g, '.')
ns = normalizedName.split "."
func = context
for n, i in ns
func = func[n]
ns.pop()
for n, i in ns
context = context[n];
if typeof func != 'function'
throw new TypeError 'Cannot execute function ' + name
func.apply(context, args)

You can call javascript function within the eval("functionname as string") either. Like below: (eval is pure javascript function)
function testfunc(){
return "hello world";
}
$( document ).ready(function() {
$("div").html(eval("testfunc"));
});
Working example: https://jsfiddle.net/suatatan/24ms0fna/4/

can i use y-combinator to get object reference for this closure?

this closure works:
var o = {
foo: 5
};
o.handler = function(obj){
return function() {
alert(obj.foo);
};
}(o);
o.handler(); //alert('5')
is it possible to define handler in-line, perhaps with something similar to a y-combinator operation?
var o = {
foo: 5,
handler: function(obj){
return function() {
alert(obj.foo);
};
}(o); //pointer to o? -----------------------------
};
out of academic curiosity, I'm not trying to do this in production code
intro to the y-combinator

No, this is not possible, because at the time of definition of the object literal, the variable o is undefined, and the this reference at the time of definition doesn't reference o.
If you used a temporary reference to this in the outer function and passed it into the closure, it would work, but you would not be able to pass in an object to get the foo property out of.
var o = {
foo: 5,
handler:function(){
var self = this;
return function() {
alert(self.foo);
};
}
};
var h = o.handler();
h();

This is not possible with an object literal by itself, as others have pointed out. However, the process can be wrapped. Wether or not it "adds anything" is debatable. This isn't the same as a Y-Combinator (perhaps half of it?), because it is not trying to give a "recursive name" (as far as I can tell Y-Combinators assume first-class functions and closures or a way to simulate such).
function bindMany (dict, res) {
res = res || {}
for (var k in dict) {
if (dict.hasOwnProperty(k)) {
var v = dict[p]
res[k] = v instanceof Function ? v(res) : v
}
}
return res
}
var o = bindMany({
foo: 5,
handler: function(obj){
return function() {
alert(obj.foo)
}
}
})
Not-tested, but shows an approach that could be taken. There are subtle issues with this and a prototype chain on dict/res, if any -- an exercise for the reader.
Happy coding.

You could just use the this keyword here:
var o = {
foo: 5,
handler: function() {
alert(this.foo);
}
};
That's a lot easier approach... Actually, your approach isn't even possible, as o is not defined when you refer to it.

We Keep Coding

JavaScript is the programming language of the Web.

How come it says array is undefined? - javascript

Here is a javascript sample: var obj = { options: [], init: function( ) { options['one'] = 'one'; for( k in options ) { alert( options[k] ); } } }; instead of prompting "one", it says undefined, why?

Related

How can I detect when an Object is getting called in JavaScript

Call a function from a variable [duplicate]

Why can't I reference an object literal from inside an object literal?

Is it possible to use a function parameter as part of a jquery statement [duplicate]

can i use y-combinator to get object reference for this closure?

Categories

Resources