I used dojo 8 years ago, so i am very new to the dojo 1.7+. I want to define a method that takes a parameter, but it also has requirements on dojo module (lang). So I tried the following.
<script>
function fillReportTable(repId) {
require(['dojo/_base/lang'], function(lang) {
//just example calls to lang..
var obj = { a:"b", c:"d" };
var thing = lang.clone(obj);
repId = repId + 1;
});
return repId;
};
alert(fillReportTable(13))
</script>
But alert(fillReportTable(13)) shows the whole function definition instead of number 14. What am i missing?
If you are going to use dojo, then almost everything need to be an AMD module and probably just a little vanilla Javascipt. So, you can turn your function into an AMD module and is easy
myApp/fillReportTable.js
define(['dojo/_base/lang'],function (lang)
{
return function fillReportTable(repId) {
var obj = { a:"b", c:"d" };
var thing = lang.clone(obj);
return repId + 1;
}
});
then, you can require it
require(["myApp/fillReportTable"], function( fillReportTable )
{
console.log(fillReportTable(123));
});
but if you continue with your approach, then you can solve it using a Promise
function fillReportTable(repId){
return new Promise(function(resolve){
require(['dojo/_base/lang'],function (lang){
var obj = { a:"b", c:"d" };
var thing = lang.clone(obj);
resolve(repId + 1);
});
});
};
How to use it
fillReportTable('Hello World').then(function(repId){
console.log(repId);
});
Note that Promise is an ECMAScript6 feature
Hope it helps
After reading this article regarding pure functions it seems to me that when working when object oriented JavaScript the concept of pure functions doesn't seem to be as simple to implement unless you want to end up calling functions with plenty of arguments or with an array of them.
Lets say I have the following function within a Javascript object.
function demo() {
var self = this;
//fixed in some other method
self.order.owner = null;
self.selectedEvent() = null;
self.order.booking_id = null;
self.order.order_id = null;
self.details = null;
self.notification = null;
self.notifyDesk = null;
self.additionalText = null;
//WILL THIS FUNCTION BE PURE?
self.test = function() {
if (self.order.owner && self.selectedEvent()) {
return true;
}
else if(self.order.booking_id == '4000' || !self.isValid(self.order.order_id) ){
return false;
}
return self.whatever;
};
return self;
}
var myDemo = new Demo();
//whatever other actions over the demo object here
console.log( myDemo.test() );
The method addOrder It is making use of 5 variables outside the function scope and belonging to the object scope.
That's not what I understood to be a "pure" function, but unless we want to call addOrder with 5 parameters, or a single array parameter with 5 elements, it doesn't seem to me we can get a pure Javascript function out of it.
This happens quite often in OO Javascript and accessing the object properties is something pretty common ?
What am I missing? Please delight me!
A pure function is one which for any input x will always produce the same output y and does not change any state. As long as the function does not break those principles, it's a pure function.
Here's an example showcasing the difference between a pure function and some impure functions:
var rect = {
width: 2,
height: 4
};
function areaPure(rectangle) {
return rectangle.width * rectangle.height;
}
function areaImpureMutate(rectangle) {
rectangle.area = rectangle.width * rectangle.height;
}
function areaImpureOuterState() {
// Uses variable declared outside of scope
return rect.width * rect.height;
}
console.log('pure:', areaPure(rect)); // no side effects
// Mutates state
areaImpureMutate(rect);
console.log('mutated:', rect.area);
// Relies on mutable state
rect.height = 5;
console.log('mutable state:', areaImpureOuterState(rect));
rect.width = 5;
console.log('mutable state:', areaImpureOuterState(rect));
The hard-and-fast rule for pure functions is that if I give you the same input regardless of the state of the rest of the program, it will always give me the same output and not mutate the state of the program directly.
So you could rewrite your test function like this to make it almost pure:
function test(obj) {
if (obj.order.owner && obj.selectedEvent()) {
return true;
}
else if(obj.order.booking_id == '4000' || !obj.isValid(obj.order.order_id) ){
return false;
}
return obj.whatever;
};
There's one problem with it: obj.selectedEvent() is an impure function which taints this pure function.
At the moment I'm implement some Javascript object in the following manner:
var graph = (function(){
var width = 200;
var height = 300;
[...]
var obj={
width: function(value){
if(value===undefined) return width;
width=value;
return obj;
},
height: function(value){
if(value===undefined) return height;
height=value;
return obj;
},[...]
};
return obj;
})();
graph.width(200)
.height(graph.width()*2);
My accessors are all defined in an extremely similar manner, mainly to allow for a sort of chaining API.
Defining the width and the height like this is really annoying, is there some sort of pattern I can use to still be able to take advantage of the closure-y stuff, without having to copy-paste the same function n times?
You could make a private object, too — not the most horrible thing in the world:
function generate(me, prop) {
return function(value) {
if(arguments.length === 0) return me[prop];
me[prop] = value;
return this;
};
}
var graph = (function() {
var me = {
width: 200,
height: 300
};
var obj = {
width: generate(me, 'width'),
height: generate(me, 'height')
};
return obj;
})();
You can write a function that generates those functions and then call it, but I can't say it's pretty since you don't have neat access to closure variables.
Please please please don't use this in production, this is just a proof of concept.
What we'll be doing here is introduce a macro into the language, that macro will be called generate . Calling generate(propName) will generate a getter in the style you want for your property. We'll wrap the code in a function, and then process the macro ourselves. This is just to prove the concept.
The syntax is something like:
var graph = Capture(function () {
var width = 200;
var height = 300;
var obj = {
width: generate(width),
height:generate(height)
};
return obj;
});
First of all:
Here is a working fiddle
What we do is the following:
1) We wrap your IIFE in a Capture function, this will process the content
var graph = Capture(function () {
[..]
});
We use string processing to peplace the generate keyword with the appropriate content
function Capture(src) {
src = src.toString()
src = src.replace(/generate\((.*?)\)/g, function (a, b) {
return "function(value){"+
"if(value===undefined){ return "+b+"; } "+b+" = value; return obj;}";
});
console.log(src)
return eval("("+src+")")();
}
We match generate(SOMETHING) and replace it with the function you want with that property. This is what the replace does.
3) We evaluate that function, and then call it
Since we evaluated it all at once, it'll have access to the closure. This gives us what we wanted and the shorter syntax.
What should we do instead?
The better alternative is to use privates with the _varName notation and avoid closure variables altogether for these purposes. This is what most libraries do, it's very clear, and you don't have these sort of problems, you can simply use bracket notation and bind for the syntactic sugar.
Ok, difficult to understand from the title only. Here is an example. I want a function to refer to a variable that is "injected" automagically, ie:
function abc() {
console.log(myVariable);
}
I have tried with:
with({myVariable: "value"}) { abc() }
but this doesn't work unless abc is declared within the with block, ie:
with({myVariable: "value"}) {
function abc() {
console.log(myVariable);
}
abc(); // This will work
}
So the last piece will work, but is it possible to fake the with statement, or do I have to force the developers to declare their function calls in a with statement?
Basically the call I want to do is:
doSomething({myVariable: "value"}, function() {
console.log(myVariable);
});
Ofcourse, I am aware I could pass this is a one parameter object, but that is not what I am trying to do:
doSomething({myVariable: "value"}, function(M) {
console.log(M.myVariable);
});
Further more, I am trying to avoid using eval:
with({myVariable: "value"}) {
eval(abc.toString())(); // Will also work
}
Is this not supported at at all beyond eval in Javascript?
JavaScript does not provide any straightforward way to achieve the syntax you're looking for. The only way to inject a variable into a Lexical Environment is by using eval (or the very similar Function constructor). Some of the answers to this question suggest this. Some other answers suggest using global variables as a workaround. Each of those solutions have their own caveats, though.
Other than that, your only option is to use a different syntax. The closest you can get to your original syntax is passing a parameter from doSomething to the callback, as Aadit M Shah suggested. Yes, I am aware you said you don't want to do that, but it's either that or an ugly hack...
Original answer (written when I didn't fully understand the question)
Maybe what you're looking for is a closure? Something like this:
var myVariable = "value";
function doSomething() {
console.log(myVariable);
};
doSomething(); // logs "value"
Or maybe this?
function createClosure(myVariable) {
return function() {
console.log(myVariable);
};
}
var closure = createClosure("value");
closure(); // logs "value"
Or even:
var closure = function(myVariable) {
return function() {
console.log(myVariable);
};
}("value");
closure(); // logs "value"
I asked a similar question a long time ago: Is it possible to achieve dynamic scoping in JavaScript without resorting to eval?
The short answer is no, you can't achieve dynamic scoping without resorting to eval. The long answer is, you don't need to.
JavaScript doesn't support dynamic scoping, but that's not an issue because you can make your free variables parameters of the function that they belong to.
In my humble opinion this is the best solution:
function doSomething(context, callback) {
callback(context);
}
doSomething({myVariable: "value"}, function(M) {
console.log(M.myVariable);
});
However since you don't want to write a formal parameter, the next best thing is to use this instead:
function doSomething(context, callback) {
callback.call(context);
}
doSomething({myVariable: "value"}, function() {
console.log(this.myVariable);
});
Another option would be to manipulate the formal parameter list of the program as follows:
function inject(func, properties) {
var args = [], params = [];
for (var property in properties) {
if (properties.hasOwnProperty(property)) {
args.push(properties[property]);
params.push(property);
}
}
return Function.apply(null, params.concat("return " + func.toString()))
.apply(null, args);
}
Now we can use this inject method to inject properties into a function as follows:
function doSomething(context, callback) {
var func = inject(callback, context);
func();
}
doSomething({myVariable: "value"}, function() {
console.log(myVariable);
});
See the demo: http://jsfiddle.net/sDKga/1/
Note: The inject function will create an entirely new function which will not have the same lexical scope as the original function. Hence functions with free variables and partially applied functions will not work as expected. Only use inject with normal functions.
The Function constructor is kind of like eval but it's much safer. Of course I would advise you to simply use a formal parameter or this instead. However the design decision is your choice.
Try:
function doSomething(vars, fun) {
for (var key in vars) { // set the variables in vars
window[key] = vars[key];
}
fun.call(); // call function
for (var key in vars) { // remove the variables again. this will allow only the function to use it
delete window[key];
}
}
Set global variables that can then be received inside of fun
The JSFiddle: http://jsfiddle.net/shawn31313/MbAMQ/
Warning: disgusting code ahead
function callWithContext(func, context, args) {
var oldProperties = {};
for(var n in context) {
if(context.hasOwnProperty(n)) {
var oldProperty = Object.getOwnPropertyDescriptor(self, n);
oldProperties[n] = oldProperty;
(function(n) {
Object.defineProperty(self, n, {
get: function() {
if(arguments.callee.caller === func) {
return context[n];
}
if(!oldProperty) {
return;
}
if(oldProperty.get) {
return oldProperty.get.apply(this, arguments);
}
return oldProperty.value;
},
set: function(value) {
if(arguments.callee.caller === func) {
context[n] = value;
}
if(!oldProperty) {
return;
}
if(oldProperty.set) {
return oldProperty.get.apply(this, arguments);
} else if(!oldProperty.writable) {
var fakeObject = {};
Object.defineProperty(fakeObject, n, {value: null, writable: false});
fakeObject[n] = value; // Kind of stupid, but…
return;
}
oldProperty.value = value;
}
});
})(n);
}
}
func.apply(this, args);
for(var n in context) {
if(context.hasOwnProperty(n)) {
if(oldProperties[n]) {
Object.defineProperty(self, n, oldProperties[n]);
} else {
delete self[n];
}
}
}
}
This is vomitously horrendous, by the way; don’t use it. But ew, it actually works.
i don't see why you can't just pass the info in or define a single global, but i think that would be best.
that said, i am working on a Module maker/runner that allows sloppy/dangerous code to execute without interference to the host environment. that provides the opportunity to re-define variables, which can be passed as an object.
this does use eval (Function() technically) but it can run in "use strict", so it's not too crazy/clever.
it doesn't leave behind artifacts.
it also won't let globals get hurt.
it's still a work in progress, and i need to iron out a couple minor details before i vouch for security, so don't use it for fort knox or anything, but it's working and stable enough to perform the operation asked for.
tested in ch28, FF22, IE10:
function Module(strCode, blnPreventExtensions, objWhitelist, objExtend) {
var __proto__=self.__proto__, pbu=self.__proto__, str=strCode, om=[].map, wasFN=false,
params = {Object:1}, fnScrubber, natives= [ Object, Array, RegExp, String, Boolean, Date] ,
nativeSlots = [],
preamble = "'use strict';" ,
inherited="__defineGetter__,__defineSetter__,__proto__,valueOf,constructor,__lookupGetter__,__lookupSetter__",
late = inherited +
Object.getOwnPropertyNames(__proto__||{}) + Object.getOwnPropertyNames(window);
late.split(",").sort().map(function(a) {
this[a] = 1;
}, params);
preamble+=";var "+inherited+";";
//turn functions into strings, but note that a function was passed
if(str.call){wasFN=true; str=String(str); delete params.Object; }
objExtend=objExtend||{};
var vals=Object.keys(objExtend).map(function(k){ return objExtend[k]; })
// build a usable clone of Object for all the new OOP methods it provides:
var fakeOb=Object.bind();
(Object.getOwnPropertyNames(Object)||Object.keys(Object)).map(function(a){
if(Object[a] && Object[a].bind){this[a]=Object[a].bind(Object); } return this;
},fakeOb)[0];
//allow "eval" and "arguments" since strict throws if you formalize them and eval is now presumed safe.
delete params.eval;
delete params.arguments;
params.hasOwnProperty=undefined;
params.toString=undefined;
params['__proto__']={};
__proto__=null;
Object.keys(objWhitelist||{}).map(function ripper(a,b){
b=this[a];
if(typeof b!=='object'){
delete this[a];
}
}, params);
// var ok=Object.keys.bind(Object);
// prevent new prototype methods from being added to native constructors:
if (blnPreventExtensions) {
natives.forEach(function(con, i) {
var proto=con.prototype;
Object.getOwnPropertyNames(proto).map(function(prop){
if(proto[prop] && proto[prop].bind ){ this[prop]=proto[prop];}
}, nativeSlots[i] = {});
delete con.constructor;
delete con.prototype.constructor;
}); //end con map()
} /* end if(blnPreventExtensions) */
//white-list harmless math utils and prevent hijacking:
delete params.Math;
if(blnPreventExtensions){Object.freeze(Math);}
//prevent literal constructors from getting Function ref (eg: [].constructor.constructor, /./.constructor.constructor, etc...):
Function.prototype.constructor = null;
try {
//generate a private wrapper function to evaluate code:
var response = Function(
Object.keys(objExtend) + (vals.length?",":"") +
Object.keys(params).filter(/./.test, /^[\w\$]+$/), // localize most globals
preamble + " return " + str.trim() // cram code into a function body with global-blocking formal parameters
);
// call it with a blank this object and only user-supplied arguments:
if (blnPreventExtensions) { //( user-land code must run inside here to be secure)
response = response.apply({}, vals.concat(fakeOb)).apply({}, [].slice.call(arguments,4) );
}else{
response = response.apply({}, vals.concat(fakeOb));
}
} catch (y) {
response = y + "!!";
} /* end try/catch */
if (blnPreventExtensions) {
om.call(natives, function(con, i) {
var pro=con.prototype;
//remove all proto methods for this con to censor any additions made by unsafe code:
Object.getOwnPropertyNames(pro).map(function(a){ try{delete pro[a];}catch(y){}});
//restore all original props from the backup:
var bu = nativeSlots[i];
om.call(Object.keys(bu), function(prop){ con.prototype[prop]=bu[prop]; }, bu);
}); //end con map()
} /* end if(blnPreventExtensions) */
//restore hidden Function constructor property:
Function.prototype.constructor = Function;
return response;
} /* end Module() */
/////////////////////////////////////////////////////////////
function doSomething(context, fn){
console.log(myVariable);
return myVariable;
}
//use 1:
alert( Module(doSomething, true, {console:1}, {myVariable: "value123"} ) );// immed
//use2:
var fn=Module(doSomething, false, {console:1}, {myVariable: "value123"} );// as function
alert(fn);
alert(fn());
again, i think OP would be best off not doing things later than need be, but for the sake of comprehensiveness and inspiration i'm putting this out there in good faith.
You need to use call() to construct a context, as in:
var f=function(){
console.log(this.foo);
};
f.call({foo:'bar'})
will print "bar"
You can avoid using eval() in calling the function, if you are willing to use it in doSomething():
function abc() {
console.log(myVariable);
}
// Prints "value"
callWith({ myVariable: "value" }, abc);
function callWith(context, func) {
for(var i in context) eval('var ' + i + ' = context[i];');
eval('(' + func.toString() + ')')();
}
Have a look at this post.
Have a look at goog.partial, scroll a little bit up to see the description of what it does:
Here is an implementation of it:
var b = goog.partial(alert, 'Hello world!');
b();//alerts "Hello world!"
In the example it passes the function alert with parameter "Hello world!" but you can pass it your own function with multiple parameters.
This allows you to create a variable that points to a function that is always called with a certain paramater. To use parameters in a function that are not named you can use arguments:
function test(){
console.log(arguments);//["hello","world"]
}
test("hello","world");
I'm working on some script for a set of functions that all operate from one call and take a large number of parameters to return one value. The main function requires the use of 11 other functions which need to work with the same parameters. I have it structured somewhat like this:
function mainfunction(param1, param2, ..., param16)
{
//do a bunch of stuff with the parameters
return output;
}
function secondaryfunction1()
{
//gets called by mainfunction
//does a bunch of stuff with the parameters from mainfunction
}
Is there anything I can do to make the parameters passed to mainfunction available to all the secondary functions without passing them or making them global variables? If not, that's fine, I'll pass them as parameters - I'm curious as to whether or not I can do it more elegantly.
You can place the definition of secondaryfunction1 inside mainfunction:
function mainfunction(param1, param2, ..., param16){
function secondaryfunction1() {
// use param1, param2, ..., param16
}
secondaryfunction1();
}
Update:
As #dystroy pointed out, this is viable if you don't need to call secondaryfunction1 somewhere else. Where the list of parameters would be coming from in this case - I don't know.
You could use arguments to pass to secondaryFunction1 all the arguments of mainfunction. But that would be silly.
What you should probably do, and what is usually done, is embed all the parameters in an "options" object :
function mainfunction(options){
secondaryfunction1(options);
}
function secondaryfunction1(options) {
// use options.param1, etc.
}
// let's call it
mainfunction({param1: 0, param2: "yes?"});
This leds to other advantages, like
naming the parameters you pass, it's not a good thing for maintenance to have to count the parameters to know which one to change. No sane library would let you pass 16 parameters as direct unnamed arguments to a function
enabling you to pass only the needed parameters (the other ones being default)
#Igor 's answer (or some variation) is the way to go. If you have to use the functions elsewhere, though (as #dystroy pointed out), then there is another possibility. Combine your parameters together into an object, and pass that object to the secondary functions.
function combineEm() {
// Get all parameters into an array.
var args = [].slice.call(arguments, 0),
output = {},
i;
// Now put them in an object
for (i = 0; i < args.length; i++) {
output["param" + i] = args[i];
}
return output;
}
From your main function, you can do:
function mainfunction(param1, param2, ..., param16) {
var params = combineEm(param1, param2, ..., param16);
var output = secondaryfunction(params);
// etc.
return output;
}
Edit: I just wanted to clarify that all of the proposed suggestions so far do work. They just each have their own trade-offs/benefits.
I tried just suggesting some changes to other answers, but ultimately I felt like I needed to just post my solution to this.
var externalFn = function(options) {
var str = options.str || 'hello world';
alert(str);
};
var main = function(options) {
var privateMethod = function() {
var str = options.str || "foobar";
alert("str: " + str);
};
// Bind a private version of an external function
var privateMethodFromExternal = externalFn.bind(this, options);
privateMethod();
privateMethodFromExternal();
};
main({ str: "abc123"});
// alerts 'str: abc123'
// alerts 'abc123'
main({});
// alerts 'str: foobar'
// alerts 'hello world'
It seems like the main point of the question is that the functions used by the 'main function' shouldn't have to keep having the options/context passed to them.
This example shows how you can use privateMethods inside the function
It also shows how you can take external functions (that you presumably use outside of main) and bind a private method version of them for use inside main.
I prefer using some sort of 'options' object, but that aspect isn't really that important to the question of scoping that the OP was really asking about. You could use 'regular' parameters as well.
This example can be found on codepen.
Here's an incredibly naughty solution, if you're interested in that sort of thing.
var f1 = function() {
var a = 1;
var _f2 = f2.toString().replace(/^function[^{}]+{/, '');
_f2 = _f2.substr(0, _f2.length - 2);
eval(_f2);
}
var f2 = function(a) {
var a = a || 0;
console.log(a);
}
f2(); // logs 0
f1(); // logs 1
It executes the contents of some external function entirely in the current scope.
However, this sort of trickery is almost definitely an indicator that your project is mis-organized. Calling external functions should usually be no more difficult than passing an object around, as dystroy's answer suggests, defining the function in-scope, as Igor's answer suggests, or by attaching some external function to this and writing your functions primarily against the properties of this. Like so:
var FunLib = {
a : 0,
do : function() {
console.log(this.a);
}
}
var Class = function() {
this.a = 1;
this.do = FunLib.do;
this.somethingThatDependsOnDo = function() {
this.a++;
this.do();
}
}
var o = new Class();
FunLib.do() // 0
o.do() // 1
o.somethingThatDependsOnDo(); // 2
o.do() // 2 now
Similarly, and possibly better-solved with a class hierarchy.
function BasicShoe {
this.steps_taken = 0;
this.max_steps = 100000;
this.doStep = function() {
this.steps_taken++;
if (this.steps_taken > this.max_steps) {
throw new Exception("Broken Shoe!");
}
}
}
function Boot {
this.max_steps = 150000;
this.kick_step_equivalent = 10;
this.doKick = function() {
for (var i = 0; i < this.kick_step_equivalent; i++) {
this.doStep();
}
}
}
Boot.prototype = new BasicShoe();
function SteelTippedBoot {
this.max_steps = 175000;
this.kick_step_equivalent = 0;
}
SteelTippedBoot.prototype = new Boot();