How to Compare 2 Functions in JavaScript

how do I compare 2 functions in javascript

var a = b = function( c ){ return c; };
//here, you can use a === b because they're pointing to the same memory and they're the same type

var a = function( c ){ return c; },
    b = function( c ){ return c; };
//here you can use that byte-saver Andy E used (which is implicitly converting the function to it's body's text as a String),

''+a == ''+b.

//this is the gist of what is happening behind the scences:

a.toString( ) == b.toString( )  

Comparing 2 functions in JavaScript

This fails because each time you do new testFn it is generating a new compareFn; you're not pointing to a reference outside of the constructor or inheriting from a prototype.

You can't access a variable from inside a Constructor with a shared function, because it doesn't have access to that closure. If you want to achieve a shared function you will need to move these values into a reference-able space too, i.e.

function testFn(name) {
    var vars = {}; // using object because javascript passes refs for objects
    this.vars = vars; // make `this.vars` point to `vars`
    vars.name = name; // set whatever on your object
}
testFn.prototype.compareFn = function () {
    console.info(this.vars.name); // can access `vars` through ref of `this.vars`
};

Now

var a = new testFn('foo'), b = new testFn('bar');
a.compareFn === b.compareFn; // true;
a.compareFn(); // logs "foo"

How to compare two functions that are called with `.bind()`?

I think the best solution here is to store a key alongside your callback inside of the array. This is a lot more reliable and way less hacky than any solution comparing functions:

register: function register(callback, key) {
        console.log('register callback');
        var obj = {
           key: key,
           callback: callback
        }
        callbackList.push(obj);
    }

you can then call remove by passing the key desired rather than the callback, and you can compare as such:

if(callbackList[0].key === key)

Just make sure you pass the desired key when registering and access the callback property within the array objects where necessary.

I think this solution using labels is much cleaner and doesn't require any confusing or strange code.

Can you compare anonymous functions in javascript?

There is no real way to compare 2 different anonymous functions for 'functionality'.

You can check if they are the same object by using your example code.

var func = function () {
    alert('hello');
};

alert(func === func);

The above will work, as you are checking to see that both objects are the same.

The only other method for comparing is to compare them as a string.

var func1 = function () {
    alert("hello");
};

var func2 = function () {
    alert('hello');
};

alert(func1.toString() === func2.toString());

Oops!, they are functionally the same, the difference is the quotes used, So this returns false.

How can I compare the values between this two functions?

If the values returned by the functions are not primitives you should:

if(!angular.equals(callmecrazier(), callmecrazy()) {
   //trigger some other function
}

EDIT
I am assuming you want to hit api at interval of 10secs and check if there are any changes, right? (else, please clarify what you are trying to achieve). If so you need to chain the async calls and then compare like below:

'use strict';

 /**
  * @ngdoc function
  * @name dashyAppApp.controller:Dashy3Ctrl
  * @description
  * # Dashy3Ctrl
  * Controller of the dashyAppApp
 */

angular.module('dashyAppApp')
 .controller('Dashy3Ctrl', function($rootScope, $scope, employees, $interval)            {
 var _this = this;

 $scope.getData = function() { // getDATA function
     return employees.getEmployees().then(function(response) {
       return response.data; 
     });

   } // End getDATA function

$scope.getData()
.then(function(data1){
   $scope.items = data1; 
   $interval(function() {
     $scope.getData()
     .then(function(data2){
        if (!angular.equals($scope.items, data1) {
          //trigger some other function
        }
     });
   }, 10000);

});

 });

Compare outcomes of two functions

Define first and second outside the this.checkCanvasWidth() . Functions create scope, so only the function you use with checkCanvasWidth has access to first and second respectively. You have to define them in the scope above those functions, so that the expect function can also see these variables.

zoomIn: {
    value: function () {
        var first,
            second;
        this.checkCanvasWidth().then(function (width) {
            first = width;
            console.log("before:" + width);
        });

        //performs a click
        this.clickZoomIn();

        this.checkCanvasWidth().then(function (width) {
            second = width;
            console.log("after:" + width);
        });

        expect(first).toBeGreaterThan(second);
    }
}

PS: if checkCanvasWidth() returns a promise, you'll have to rewrite this whole function, since you want to do the expect() call AFTER first and second ahve been set.

Promise version:

zoomIn: {
    value: function () {
        var first,
            second;
        this.checkCanvasWidth().then(function (width) {
            first = width;
            console.log("before:" + width);
            if (first && second) {
                expect(first).toBeGreaterThan(second);
            }
        });

        //performs a click
        this.clickZoomIn();

        this.checkCanvasWidth().then(function (width) {
            second = width;
            if (first && second) {
                expect(first).toBeGreaterThan(second);
            }
        });
    }
}

Comparing two functions in JavaScript

You mixed up value and innerHTML.

value is used for input and textarea elements and innerHTML is for almost other element

This code will work for you:

<!DOCTYPE html>
<html>
<body>
<h1>Practice Spelling Test</h1>
<p id="aWord"></p>

<input id="yourTurn">

<button onclick="myFunction()">New Word</button>
<button onclick="checkSpelling()">Check My Spelling</button>

<p id="result"></p>

<script>

var sightWord = ["hoof", "hook", "shook", "hood", "wood", "took", "book", "good", "food", "mood", "look"];
var yourTurn = document.getElementById("yourTurn");
var aWord = document.getElementById("aWord");

function myFunction() {
    var showWord = sightWord[Math.floor((Math.random()*10)+1)];
    aWord.innerHTML = showWord;
}

function checkSpelling(result) {

  var checkWord = (yourTurn.value == aWord.innerHTML)?"Nice Job!":"So close! Try again!";
    document.getElementById("result").innerHTML=checkWord;
}

</script>

</body>
</html>

See live code here: http://jsbin.com/ubofus/1/edit

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