I have a function to clear the user text,but the clearText function is inside the function and variable.
I find some information on Internet,but some solutions are only solve the function in variable and have not two function.
Can anyone tell me how I would call the function in function and variable,please?
And I am sorry about grammar ,English is not my mother language.I am hard to translate using google translate.
Calling a JavaScript function named in a variable
I try it but got undefined.
<script>
var testing = (function(){
function clearText(){
/* call other function in this testing function */
}
/* other function */
})();
function resetInput() {
/* I call clearText() function here */
}
</script>
Unless your first function returns clearText (or makes it accessible outside of that function in some other way), you cannot use it in resetInput.
If it does return clearText, then you can use it via testing:
var testing = (function(){
function clearText(){
console.log('clearText() triggered');
/* some code*/
}
/* some function */
return clearText; // ****
})();
function resetInput() {
testing(); // ****
}
resetInput();
If it makes clearText available in some other way (a global variable, etc.), how you'd use it would depend on what that other way is.
What you are using is IIFE (immediately Invoked Function Expression). What you do in the following code is inserting the return of nothing into the variable testing.
Execute the following :
var testing = (function() {
function clearText() {
console.log('clearText execution');
}
})();
console.log(testing);
Now what if we return something :
var testing = (function() {
function clearText() {
console.log('clearText execution');
}
return 'try';
})();
console.log(testing);
If you want to execute the function clearText outside of the IIFE, you have to return a pointer to it, like :
var testing = (function() {
function clearText() {
console.log('clearText execution');
return 'done';
}
return clearText;
})();
console.log(testing);
console.log(testing());
Now, there is no need for IIFE, you could just store the function inside of object and use the reference :
var testing = {
clearText: () => {
console.log('clearText execution');
return 'done';
}
};
function resetInput() {
testing.clearText()
}
resetInput();
I want to do something like this:
var build= (function(){
//my function body
})();
function test(){
//somthing then call build
build() //i want to call build function again in my code
}
How can I do this?
I tried this in angular:
var buildRoot = (() => {
$SubNode.get({
TypeID: vendorAdminService.NodeType.Category
}, function(data: vendorAdminService.IGetNodeParameters) {
$scope.ProductTree = data.TreeNodeModelItem;
$scope.AjaxLoading = false;
}, function(err) {
// alert(err)
})
})();
$mdDialog.show(confirm).then(function() {
$Category.Remove(node.ID)
buildRoot
}, function() {
});
but it does not work.
Anybody can guide me??
You need to return a function in your IIFE.
If you IIF is not trivial and has many functionalities you could also consider using Reveal Module Pattern.
var build = (function() {
var f = function() {
console.log('hello');
};
f();
return f;
})();
function test() {
build();
}
test();
Just use a named function.
Your IIFE needs to return a function, for later calling. But then is no need for an anonymous function.
function build() {
//my function body
}
or
var build = function () {
//my function body
};
var build = (function() {
var init = function() {
// magic code
};
return {
init: init
}
}());
function test() {
build.init()
}
test();
You include all your functionalities inside your build object, and you'll be able to call them as soon as you return them from inside that object. This effectively is called the revealing module pattern
For more information, read this
I see that there are missing semi-colons ";"
$mdDialog.show(confirm).then(function() {
$Category.Remove(node.ID);
buildRoot();
}, function() {
});
I'm self-teaching myself JavaScript and out of curiosity I'm wondering what is the proper way of returning a value from one function to be used in another function. For example:
function firstFunction() {
// do something;
return somevalue
}
So how do I set up the second function to use somevalue? Thanks.
Call the function and save the return value of that very call.
function firstFunction() {
// do something
return "testing 123";
}
var test = firstFunction(); // this will grab you the return value from firstFunction();
alert(test);
You can make this call from another function too, as long as both functions have same scope.
For example:
function testCase() {
var test = firstFunction();
alert(test);
}
Demo
You could call firstFunction from secondFunction :
function secondFunction() {
alert(firstFunction());
}
Or use a global variable to host the result of firstFunction :
var v = firstFunction();
function secondFunction() { alert(v); }
Or pass the result of firstFunction as a parameter to secondFunction :
function secondFunction(v) { alert(v); }
secondFunction(firstFunction());
Or pass firstFunction as a parameter to secondFunction :
function secondFunction(fn) { alert(fn()); }
secondFunction(firstFunction);
Here is a demo : http://jsfiddle.net/wared/RK6X7/.
Call function within other function :
function abc(){
var a = firstFunction();
}
function firstFunction() {
Do something;
return somevalue
}
You can do this for sure. Have a look below
function fnOne(){
// do something
return value;
}
function fnTwo(){
var strVal= fnOne();
//use strValhere
alert(strVal);
}
var captcha = '';
//function name one
function one(captcha){
var captcha = captcha;
//call another function and pass variable data
var captcha = firstFunction(captcha);
};
// second function name
function firstFunction(captcha){
alert(captcha);
}
To copy the return value of any javascript(in chrome console), we can use inbuilt copy() method.
you can use any expression, function, etc
find some examples below
using expresseion
a = 245;
copy(a);
using function
a = function() {
return "Hello world!"
}
copy(a());
Official Doc for reference
I need to create a function which can be executed only once, in each time after the first it won't be executed. I know from C++ and Java about static variables that can do the work but I would like to know if there is a more elegant way to do this?
If by "won't be executed" you mean "will do nothing when called more than once", you can create a closure:
var something = (function() {
var executed = false;
return function() {
if (!executed) {
executed = true;
// do something
}
};
})();
something(); // "do something" happens
something(); // nothing happens
In answer to a comment by #Vladloffe (now deleted): With a global variable, other code could reset the value of the "executed" flag (whatever name you pick for it). With a closure, other code has no way to do that, either accidentally or deliberately.
As other answers here point out, several libraries (such as Underscore and Ramda) have a little utility function (typically named once()[*]) that accepts a function as an argument and returns another function that calls the supplied function exactly once, regardless of how many times the returned function is called. The returned function also caches the value first returned by the supplied function and returns that on subsequent calls.
However, if you aren't using such a third-party library, but still want a utility function (rather than the nonce solution I offered above), it's easy enough to implement. The nicest version I've seen is this one posted by David Walsh:
function once(fn, context) {
var result;
return function() {
if (fn) {
result = fn.apply(context || this, arguments);
fn = null;
}
return result;
};
}
I would be inclined to change fn = null; to fn = context = null;. There's no reason for the closure to maintain a reference to context once fn has been called.
Usage:
function something() { /* do something */ }
var one_something = once(something);
one_something(); // "do something" happens
one_something(); // nothing happens
[*] Be aware, though, that other libraries, such as this Drupal extension to jQuery, may have a function named once() that does something quite different.
Replace it with a reusable NOOP (no operation) function.
// this function does nothing
function noop() {};
function foo() {
foo = noop; // swap the functions
// do your thing
}
function bar() {
bar = noop; // swap the functions
// do your thing
}
Point to an empty function once it has been called:
function myFunc(){
myFunc = function(){}; // kill it as soon as it was called
console.log('call once and never again!'); // your stuff here
};
<button onClick=myFunc()>Call myFunc()</button>
Or, like so:
var myFunc = function func(){
if( myFunc.fired ) return;
myFunc.fired = true;
console.log('called once and never again!'); // your stuff here
};
// even if referenced & "renamed"
((refToMyfunc)=>{
setInterval(refToMyfunc, 1000);
})(myFunc)
UnderscoreJs has a function that does that, underscorejs.org/#once
// Returns a function that will be executed at most one time, no matter how
// often you call it. Useful for lazy initialization.
_.once = function(func) {
var ran = false, memo;
return function() {
if (ran) return memo;
ran = true;
memo = func.apply(this, arguments);
func = null;
return memo;
};
};
Talking about static variables, this is a little bit like closure variant:
var once = function() {
if(once.done) return;
console.log('Doing this once!');
once.done = true;
};
once(); // Logs "Doing this once!"
once(); // Logs nothing
You could then reset a function if you wish:
once.done = false;
once(); // Logs "Doing this once!" again
You could simply have the function "remove itself"
function Once(){
console.log("run");
Once = undefined;
}
Once(); // run
Once(); // Uncaught TypeError: undefined is not a function
But this may not be the best answer if you don't want to be swallowing errors.
You could also do this:
function Once(){
console.log("run");
Once = function(){};
}
Once(); // run
Once(); // nothing happens
I need it to work like smart pointer, if there no elements from type A it can be executed, if there is one or more A elements the function can't be executed.
function Conditional(){
if (!<no elements from type A>) return;
// do stuff
}
var quit = false;
function something() {
if(quit) {
return;
}
quit = true;
... other code....
}
simple decorator that easy to write when you need
function one(func) {
return function () {
func && func.apply(this, arguments);
func = null;
}
}
using:
var initializer= one( _ =>{
console.log('initializing')
})
initializer() // 'initializing'
initializer() // nop
initializer() // nop
try this
var fun = (function() {
var called = false;
return function() {
if (!called) {
console.log("I called");
called = true;
}
}
})()
From some dude named Crockford... :)
function once(func) {
return function () {
var f = func;
func = null;
return f.apply(
this,
arguments
);
};
}
Reusable invalidate function which works with setInterval:
var myFunc = function (){
if (invalidate(arguments)) return;
console.log('called once and never again!'); // your stuff here
};
const invalidate = function(a) {
var fired = a.callee.fired;
a.callee.fired = true;
return fired;
}
setInterval(myFunc, 1000);
Try it on JSBin: https://jsbin.com/vicipar/edit?js,console
Variation of answer from Bunyk
Here is an example JSFiddle - http://jsfiddle.net/6yL6t/
And the code:
function hashCode(str) {
var hash = 0, i, chr, len;
if (str.length == 0) return hash;
for (i = 0, len = str.length; i < len; i++) {
chr = str.charCodeAt(i);
hash = ((hash << 5) - hash) + chr;
hash |= 0; // Convert to 32bit integer
}
return hash;
}
var onceHashes = {};
function once(func) {
var unique = hashCode(func.toString().match(/function[^{]+\{([\s\S]*)\}$/)[1]);
if (!onceHashes[unique]) {
onceHashes[unique] = true;
func();
}
}
You could do:
for (var i=0; i<10; i++) {
once(function() {
alert(i);
});
}
And it will run only once :)
Initial setup:
var once = function( once_fn ) {
var ret, is_called;
// return new function which is our control function
// to make sure once_fn is only called once:
return function(arg1, arg2, arg3) {
if ( is_called ) return ret;
is_called = true;
// return the result from once_fn and store to so we can return it multiply times:
// you might wanna look at Function.prototype.apply:
ret = once_fn(arg1, arg2, arg3);
return ret;
};
}
If your using Node.js or writing JavaScript with browserify, consider the "once" npm module:
var once = require('once')
function load (file, cb) {
cb = once(cb)
loader.load('file')
loader.once('load', cb)
loader.once('error', cb)
}
If you want to be able to reuse the function in the future then this works well based on ed Hopp's code above (I realize that the original question didn't call for this extra feature!):
var something = (function() {
var executed = false;
return function(value) {
// if an argument is not present then
if(arguments.length == 0) {
if (!executed) {
executed = true;
//Do stuff here only once unless reset
console.log("Hello World!");
}
else return;
} else {
// otherwise allow the function to fire again
executed = value;
return;
}
}
})();
something();//Hello World!
something();
something();
console.log("Reset"); //Reset
something(false);
something();//Hello World!
something();
something();
The output look like:
Hello World!
Reset
Hello World!
A simple example for turning on light only once.
function turnOnLightOnce() {
let lightOn = false;
return function () {
if (!lightOn) {
console.log("Light is not on...Turning it on for first and last time");
lightOn = true;
}
};
}
const lightOn = turnOnLightOnce();
lightOn() // Light is not on...Turning it on for first and last time
lightOn()
lightOn()
lightOn()
lightOn()
https://codesandbox.io/s/javascript-forked-ojo0i?file=/index.js
This happens due to closure in JavaScript.
function once (fn1) {
var ran = false
var memo = null
var fn = function(...args) {
if(ran) {return memo}
ran = true
memo = fn1.apply(null, args)
return memo
}
return fn
}
I'm using typescript with node and it was #I Hate Lazy's answer that inspired me. I just assigned my function to a noop function.
let printName = (name: string) => {
console.log(name)
printName = () => {}
}
printName('Sophia') // Sophia
printName('Nico') // Nothing Happens
https://jsbin.com/yuzicek/edit?js,console
FOR EVENT HANDLER
If the function is a callback for an event listener, there is already a built-in option in the addEventListner method for just executing the callback once.
It can accept 3 parameters
Type
callback
options
options is an object that has a property called once
ex:
const button = document.getElementById('button');
const callbackFunc = () => {
alert('run')
}
button.addEventListener('click', callbackFunc, { once: true })
<button id="button">Click Once</button>
Trying to use underscore "once" function:
var initialize = _.once(createApplication);
initialize();
initialize();
// Application is only created once.
http://underscorejs.org/#once
var init = function() {
console.log("logges only once");
init = false;
};
if(init) { init(); }
/* next time executing init() will cause error because now init is
-equal to false, thus typing init will return false; */
if (!window.doesThisOnce){
function myFunction() {
// do something
window.doesThisOnce = true;
};
};
If you're using Ramda, you can use the function "once".
A quote from the documentation:
once Function
(a… → b) → (a… → b)
PARAMETERS
Added in v0.1.0
Accepts a function fn and returns a function that guards invocation of fn such that fn can only ever be called once, no matter how many times the returned function is invoked. The first value calculated is returned in subsequent invocations.
var addOneOnce = R.once(x => x + 1);
addOneOnce(10); //=> 11
addOneOnce(addOneOnce(50)); //=> 11
keep it as simple as possible
function sree(){
console.log('hey');
window.sree = _=>{};
}
You can see the result
JQuery allows to call the function only once using the method one():
let func = function() {
console.log('Calling just once!');
}
let elem = $('#example');
elem.one('click', func);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div>
<p>Function that can be called only once</p>
<button id="example" >JQuery one()</button>
</div>
Implementation using JQuery method on():
let func = function(e) {
console.log('Calling just once!');
$(e.target).off(e.type, func)
}
let elem = $('#example');
elem.on('click', func);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div>
<p>Function that can be called only once</p>
<button id="example" >JQuery on()</button>
</div>
Implementation using native JS:
let func = function(e) {
console.log('Calling just once!');
e.target.removeEventListener(e.type, func);
}
let elem = document.getElementById('example');
elem.addEventListener('click', func);
<div>
<p>Functions that can be called only once</p>
<button id="example" >ECMAScript addEventListener</button>
</div>
Tossing my hat in the ring for fun, added advantage of memoizing
const callOnce = (fn, i=0, memo) => () => i++ ? memo : (memo = fn());
// usage
const myExpensiveFunction = () => { return console.log('joe'),5; }
const memoed = callOnce(myExpensiveFunction);
memoed(); //logs "joe", returns 5
memoed(); // returns 5
memoed(); // returns 5
...
You can use IIFE. IIFE means Immediately Invoked Function Expression and the result is to call a function only once by the time is created.
Your code will be like this:
(function () {
//The code you want to execute only one time etc...
console.log("Hello world");
})()
Additionally, this way the data in the function remains encapsulated.
Of course and you can return values from the function and stored them into a new variable, by doing:
const/let value = (function () {
//The code you want to execute only one time etc...
const x = 10;
return x;
})()
function x()
{
let a=0;
return function check()
{
if(!a++)
{
console.log("This Function will execute Once.")
return;
}
console.log("You Can't Execute it For the Second Time.")
return;
}
}
z=x()
z() //Op - This Function will execute once
z() //OP - You can't Execute it for the second time.
I find it useful to just have a simple function that just returns true once, so you can keep the side effects higher up.
let once = () => !! (once = () => false);
once() // true
once() // false
Use like this:
if (once()) {
sideEffect()
}
This exploits the fact that you can coerce an assignment expression to return true while changing the same function into a function that returns false.
If you must have it execute a function, it can be adapted using a ternary:
let once = (x) => !! (once = () => false) ? x() : false;
Now it accepts a single function as an argument. Fun fact, the second false is never reached.
// This is how function in JavaScript can be called only once
let started = false;
if (!started) {
start() { // "do something" }
}
started = true;
}
I have written the following function.
function obj()
{
this.a;
}
obj.prototype.catch = function()
{
alert('Catched')
}
obj.prototype.do = function()
{
alert('called');
}
What i need is, to call obj::catch() after obj::do() is called and the call must be performed from inside obj::do()
So how to pass the local function of obj to setTimeout
i have tried
obj.prototype.do = function()
{
window.setTimeout('"'+this.catch+'()"',1000);
alert('called');
}
It does not worked
Then i tried
obj.prototype.do = function()
{
window.setTimeout('"'+this+'.catch()"',1000);
alert('called');
}
which gave me the following error on Chrome console
Uncaught SyntaxError: Unexpected token ILLEGAL
So i tried the following dirty method(is it really dirty ?)
obj.prototype.do = function()
{
this.pid = randomVal(100);
window['temp'+this.pid] = this;
window.setTimeout("temp"+this.pid+".catch();",1000);
alert('called');
}
function randomVal(bound)//returns a random number between 0 and <bound>
{
return (Math.floor(Math.random()*(bound)));
}
That worked.
so why the first two methods not worked.Is there any other way to do the same thing without global variables..
The second method and last method are almost similar .But why am i gettng the error in second method..?
The worked code can be found here
http://jsfiddle.net/jXhAs/
Don't pass strings to setTimeout … ever.
var self = this; // Because the scope will change
setTimeout(function () { self.catch() },1000);
Or if you are using JS 1.8.5:
setTimeout(this.catch.bind(this),1000);
You can read more about bind
You should pass a function to setTimeout (not a string):
Example:
var self = this;
setTimeout(function(){
self.catch();
},1000);
use a closure
obj.prototype.do = function()
{
window.setTimeout((function(that){
return function(){
that.catch();
};
})(this),1000);
alert('called');
}
Why go through all of this effort, just pass the function.
function obj() {
this.a;
}
obj.prototype.
catch = function() {
alert('Catched')
}
obj.prototype.do = function() {
setTimeout(this.
catch, 1000);
}
var test = new obj();
test.do();