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Anonymous function argument

I have a section in my code that looks like this
var locationDefer = $.Deferred();
if (saSel.Company === -1) {
database.getAllLocations().then(function (result) {
var locations = JSON.parse(result.d);
locationDefer.resolve(locations);
});
} else {
database.getLocationsForCompany(saSel.Company).then(function (result) {
var locations = JSON.parse(result.d);
locationDefer.resolve(locations);
});
}
However, since it is basically the same thing twice, just with a different ajax call - is there any way to either have the anonymous function part
function (result) {
var locations = JSON.parse(result.d);
locationDefer.resolve(locations);
})
declared as a real function and then just called in the .then() clause, or can I somehow provide the to-be-called-function of the database object?
For the latter, I had something in my mind that could look like this, but I have no clue how to do the last line.
if(saSel.Company === -1) {
fun = 'getAllLocations';
arg = null;
} else {
fun = 'getLocationsForCompany';
arg = saSel.Company;
}
// database.fun(arg).then(function (result) {...});

You can define a function and pass its reference as success callback handler
//Define the function handler
function resultHandler(result) {
var locations = JSON.parse(result.d);
locationDefer.resolve(locations);
}
if (saSel.Company === -1) {
fun = 'getAllLocations';
arg = null;
} else {
fun = 'getLocationsForCompany';
arg = saSel.Company;
}
//Invoke the method using Bracket notation
//And, pass the success handler as reference
database[fun](arg).then(resultHandler);
Additionally, as getLocationsForCompany() and getAllLocations() returns a promise, you shouldn't use $.Deferred() directly return Promise
return database[fun](arg);

Adding Dynamic Parameter to a function with parameter which is passed as parameter to current function

I will walk across the scenario about what i am trying to do:
I pass a function with parameter as a parameter to a function. This function will add an additional parameter to the passed function and then make a call to a function.
For ex:
funcA(function(){ funcB("add Me") }) // call to funcA
funcA : function( fn ){
var additionalParams = "add Me too"
}
funcB : function( str1,str2){ //gets me both strings }
I looked here and thought this is what i wanted but did not help.
Here is the jsfiddle i tried.

is not necessary call apply method. just declare an parameter on function passed to funcA
funcA = function( fn ){
var additionalParams = "add Me too";
fn(additionalParams);
}
funcA(function(str){
funcB("add Me", str);
});
funcB = function( str1,str2){ //gets me both strings };
update
your jsfiddle code modified like i said.
function appendArguments(fn) {
var slice = Array.prototype.slice.call.bind(Array.prototype.slice),
args = slice(arguments, 1);
return function (t) {
return fn(t);
};
}
var bar = appendArguments(function(t){foo(1, t)});
bar(2);
function foo (x,y){
alert(x);
alert(y);
}
try yourself. it works for me.

How to use a return value in another function in Javascript?

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

Function in JavaScript that can be called only once

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;
}

Javascript callback function and parameters [duplicate]

This question already has answers here:
Pass an extra argument to a callback function
(5 answers)
Closed 6 years ago.
I want to something similar to this:
function AjaxService()
{
this.Remove = function (id, call_back)
{
myWebService.Remove(id, CallBack)
}
function CallBack(res) {
call_back(res);
}
}
so my calling program will be like this:
var xx = new AjaxService();
xx.Remove(1,success);
function success(res)
{
}
Also if I want to add more parameters to success function how will I achieve it.
Say if I have success function like this:
var xx = new AjaxService();
//how to call back success function with these parameters
//xx.Remove(1,success(22,33));
function success(res,val1, val2)
{
}
Help will be appreciated.

Use a closure and a function factory:
function generateSuccess (var1,var2) {
return function (res) {
// use res, var1 and var2 in here
}
}
xx.Remove(1,generateSuccess(val1,val2));
What you're passing here is not the generateSuccess function but the anonymous function returned by generateSuccess that looks like the callback expected by Remove. val1 and val2 are passed into generateSuccess and captured by a closure in the returned anonymous function.
To be more clear, this is what's happening:
function generateSuccess (var1,var2) {
return function (res) {
// use res, var1 and var2 in here
}
}
var success = generateSuccess(val1,val2);
xx.Remove(1,success);
Or if you prefer to do it inline:
xx.Remove(1,(function(var1,var2) {
return function (res) {
// this is your success function
}
})(val1,val2));
not as readable but saves you from naming the factory function. If you're not doing this in a loop then Xinus's solution would also be fine and simpler than my inline version. But be aware that in a loop you need the double closure mechanism to disconnect the variable passed into the callback function from the variable in the current scope.

You can pass it as anonymous function pointer
xx.Remove(1,function(){
//function call will go here
success(res,val1, val2);
});

one way to do this:
function AjaxService {
var args_to_cb = [];
this.Remove = function (id, call_back, args_to_callback_as_array) {
if( args_to_callback_as_array!=undefined )
args_to_cb = args_to_callback_as_array;
else
args_to_cb = [];
myWebService.Remove(id, CallBack)
}
function CallBack(res) {
setTimeout( function(){ call_back(res, args_to_cb); }, 0 );
}
}
So you can use it like this:
var service = new AjaxService();
service.Remove(1,success, [22,33]);
function success(res,val1, val2)
{
alert("result = "+res);
alert("values are "+val1+" and "+val2);
}
I usually have the callback execute using a setTimeout. This way, your callback will execute when it gets the time to do so. Your code will continue to execute meanwhile, e.g:
var service = new AjaxService();
service.remove(1, function(){ alert('done'); }); // alert#1
alert('called service.remove'); // alert#2
Your callback will execute after alert#2.
Of course, in case of your application, it will happen so automatically since the ajax callback itself is asynchronous. So in your application, you had better not do this.
Cheers!
jrh