How to check if two arrays are equal with JavaScript?

var a = [1, 2, 3];
var b = [3, 2, 1];
var c = new Array(1, 2, 3);

alert(a == b + "|" + b == c);

demo

How can I check these array for equality and get a method which returns true if they are equal?

Does jQuery offer any method for this?

22 thoughts on “How to check if two arrays are equal with JavaScript?”

  1. [2021 changelog: bugfix for option4: no total ordering on js objects (even excluding NaN!=NaN and '5'==5 ('5'===5, '2'<3, etc.)), so cannot use .sort on Map.keys() (though you can on Object.keys(obj), since even ‘numerical’ keys are strings)]

    Option 1

    Easiest option, works in almost all cases, except that null!==undefined but they both are converted to JSON representation null and considered equal:

    function arraysEqual(a1,a2) {
        /* WARNING: arrays must not contain {objects} or behavior may be undefined */
        return JSON.stringify(a1)==JSON.stringify(a2);
    }
    

    (This might not work if your array contains objects. Whether this still works with objects depends on whether the JSON implementation sorts keys. For example, the JSON of {1:2,3:4} may or may not be equal to {3:4,1:2}; this depends on the implementation, and the spec makes no guarantee whatsoever. [2017 update: Actually the ES6 specification now guarantees object keys will be iterated in order of 1) integer properties, 2) properties in the order they were defined, then 3) symbol properties in the order they were defined. Thus IF the JSON.stringify implementation follows this, equal objects (in the === sense but NOT NECESSARILY in the == sense) will stringify to equal values. More research needed. So I guess you could make an evil clone of an object with properties in the reverse order, but I cannot imagine it ever happening by accident…] At least on Chrome, the JSON.stringify function tends to return keys in the order they were defined (at least that I’ve noticed), but this behavior is very much subject to change at any point and should not be relied upon. If you choose not to use objects in your lists, this should work fine. If you do have objects in your list that all have a unique id, you can do a1.map(function(x)}{return {id:x.uniqueId}}). If you have arbitrary objects in your list, you can read on for option #2.)

    This works for nested arrays as well.

    It is, however, slightly inefficient because of the overhead of creating these strings and garbage-collecting them.


    Option 2

    More "proper" option, which you can override to deal with special cases (like regular objects and null/undefined and custom objects, if you so desire):

    // generally useful functions
    function type(x) { // does not work in general, but works on JSONable objects we care about... modify as you see fit
        // e.g.  type(/asdf/g) --> "[object RegExp]"
        return Object.prototype.toString.call(x);
    }
    function zip(arrays) {
        // e.g. zip([[1,2,3],[4,5,6]]) --> [[1,4],[2,5],[3,6]]
        return arrays[0].map(function(_,i){
            return arrays.map(function(array){return array[i]})
        });
    }
    

     

    // helper functions
    function allCompareEqual(array) {
        // e.g.  allCompareEqual([2,2,2,2]) --> true
        // does not work with nested arrays or objects
        return array.every(function(x){return x==array[0]});
    }
    
    function isArray(x){ return type(x)==type([]) }
    function getLength(x){ return x.length }
    function allTrue(array){ return array.reduce(function(a,b){return a&&b},true) }
        // e.g. allTrue([true,true,true,true]) --> true
        // or just array.every(function(x){return x});
    

     

    function allDeepEqual(things) {
        // works with nested arrays
        if( things.every(isArray) )
            return allCompareEqual(things.map(getLength))     // all arrays of same length
                   && allTrue(zip(things).map(allDeepEqual)); // elements recursively equal
    
        //else if( this.every(isObject) )
        //  return {all have exactly same keys, and for 
        //          each key k, allDeepEqual([o1[k],o2[k],...])}
        //  e.g. ... && allTrue(objectZip(objects).map(allDeepEqual)) 
    
        //else if( ... )
        //  extend some more
    
        else
            return allCompareEqual(things);
    }
    

    Demo:

    allDeepEqual([ [], [], [] ])
    true
    allDeepEqual([ [1], [1], [1] ])
    true
    allDeepEqual([ [1,2], [1,2] ])
    true
    allDeepEqual([ [[1,2],[3]], [[1,2],[3]] ])
    true
    
    allDeepEqual([ [1,2,3], [1,2,3,4] ])
    false
    allDeepEqual([ [[1,2],[3]], [[1,2],[],3] ])
    false
    allDeepEqual([ [[1,2],[3]], [[1],[2,3]] ])
    false
    allDeepEqual([ [[1,2],3], [1,[2,3]] ])
    false
    

    To use this like a regular function, do:

    function allDeepEqual2() {
        return allDeepEqual([].slice.call(arguments));
    }
    

    Demo:

    allDeepEqual2([[1,2],3], [[1,2],3])
    true
    

    Options 3

    edit: It’s 2016 and my previous overcomplicated answer was bugging me. This recursive, imperative "recursive programming 101" implementation keeps the code really simple, and furthermore fails at the earliest possible point (giving us efficiency). It also doesn’t generate superfluous ephemeral datastructures (not that there’s anything wrong with functional programming in general, but just keeping it clean here).

    If we wanted to apply this to a non-empty arrays of arrays, we could do seriesOfArrays.reduce(arraysEqual).

    This is its own function, as opposed to using Object.defineProperties to attach to Array.prototype, since that would fail with a key error if we passed in an undefined value (that is however a fine design decision if you want to do so).

    This only answers OPs original question.

    function arraysEqual(a,b) {
        /*
            Array-aware equality checker:
            Returns whether arguments a and b are == to each other;
            however if they are equal-lengthed arrays, returns whether their 
            elements are pairwise == to each other recursively under this
            definition.
        */
        if (a instanceof Array && b instanceof Array) {
            if (a.length!=b.length)  // assert same length
                return false;
            for(var i=0; i<a.length; i++)  // assert each element equal
                if (!arraysEqual(a[i],b[i]))
                    return false;
            return true;
        } else {
            return a==b;  // if not both arrays, should be the same
        }
    }
    

    Examples:

    arraysEqual([[1,2],3], [[1,2],3])
    true
    arraysEqual([1,2,3], [1,2,3,4])
    false
    arraysEqual([[1,2],[3]], [[1,2],[],3])
    false
    arraysEqual([[1,2],[3]], [[1],[2,3]])
    false
    arraysEqual([[1,2],3], undefined)
    false
    arraysEqual(undefined, undefined)
    true
    arraysEqual(1, 2)
    false
    arraysEqual(null, null)
    true
    arraysEqual(1, 1)
    true
    arraysEqual([], 1)
    false
    arraysEqual([], undefined)
    false
    arraysEqual([], [])
    true
    

    If you wanted to apply this to JSON-like data structures with js Objects, you could do so. Fortunately we’re guaranteed that all objects keys are unique, so iterate over the objects OwnProperties and sort them by key, then assert that both the sorted key-array is equal and the value-array are equal, and just recurse. We can extend this to include Maps as well (where the keys are also unique). (However if we extend this to Sets, we run into the tree isomorphism problem http://logic.pdmi.ras.ru/~smal/files/smal_jass08_slides.pdf – fortunately it’s not as hard as general graph isomorphism; there is in fact an O(#vertices) algorithm to solve it, but it can get very complicated to do it efficiently. The pathological case is if you have a set made up of lots of seemingly-indistinguishable objects, but upon further inspection some of those objects may differ as you delve deeper into them. You can also work around this by using hashing to reject almost all cases.)


    Option 4:
    (continuation of 2016 edit)

    This should work with most objects:

    const STRICT_EQUALITY = (a,b)=> a===b;
    function deepEquals(a,b, areEqual=STRICT_EQUALITY) {
        /* compares objects hierarchically using the provided 
           notion of equality (defaulting to ===);
           supports Arrays, Objects, Maps, ArrayBuffers */
        if (a instanceof Array && b instanceof Array)
            return arraysEqual(a,b, areEqual);
        if (Object.getPrototypeOf(a)===Object.prototype && Object.getPrototypeOf(b)===Object.prototype)
            return objectsEqual(a,b, areEqual);
        if (a instanceof Map && b instanceof Map)
            return mapsEqual(a,b, areEqual);        
        if (a instanceof Set && b instanceof Set) {
            if (areEquals===STRICT_EQUALITY)
                return setsEqual(a,b);
            else
                throw "Error: set equality by hashing not implemented because cannot guarantee custom notion of equality is transitive without programmer intervention."
        }
        if ((a instanceof ArrayBuffer || ArrayBuffer.isView(a)) && (b instanceof ArrayBuffer || ArrayBuffer.isView(b)))
            return typedArraysEqual(a,b);
        return areEqual(a,b);  // see note[1] -- IMPORTANT
    }
    
    function arraysEqual(a,b, areEqual) {
        if (a.length!=b.length)
            return false;
        for(var i=0; i<a.length; i++)
            if (!deepEquals(a[i],b[i], areEqual))
                return false;
        return true;
    }
    function objectsEqual(a,b, areEqual) {
        var aKeys = Object.getOwnPropertyNames(a);
        var bKeys = Object.getOwnPropertyNames(b);
        if (aKeys.length!=bKeys.length)
            return false;
        aKeys.sort();
        bKeys.sort();
        for(var i=0; i<aKeys.length; i++)
            if (!areEqual(aKeys[i],bKeys[i])) // keys must be strings
                return false;
        return deepEquals(aKeys.map(k=>a[k]), aKeys.map(k=>b[k]), areEqual);
    }
    function mapsEqual(a,b, areEqual) { // assumes Map's keys use the '===' notion of equality, which is also the assumption of .has and .get methods in the spec; however, Map's values use our notion of the areEqual parameter
        if (a.size!=b.size)
            return false;
        return [...a.keys()].every(k=> 
            b.has(k) && deepEquals(a.get(k), b.get(k), areEqual)
        );
    }
    function setsEqual(a,b) {
        // see discussion in below rest of StackOverflow answer
        return a.size==b.size && [...a.keys()].every(k=> 
            b.has(k)
        );
    }
    function typedArraysEqual(a,b) {
        // we use the obvious notion of equality for binary data
        a = new Uint8Array(a);
        b = new Uint8Array(b);
        if (a.length != b.length)
            return false;
        for(var i=0; i<a.length; i++)
            if (a[i]!=b[i])
                return false;
        return true;
    }
    

    Demo (not extensively tested):

    var nineTen = new Float32Array(2);
    nineTen[0]=9; nineTen[1]=10;
    
    > deepEquals(
        [[1,[2,3]], 4, {a:5,'111':6}, new Map([['c',7],['d',8]]), nineTen],
        [[1,[2,3]], 4, {111:6,a:5}, new Map([['d',8],['c',7]]), nineTen]
    )
    true
    
    > deepEquals(
        [[1,[2,3]], 4, {a:'5','111':6}, new Map([['c',7],['d',8]]), nineTen],
        [[1,[2,3]], 4, {111:6,a:5}, new Map([['d',8],['c',7]]), nineTen],
        (a,b)=>a==b
    )
    true
    

    Note that if one is using the == notion of equality, then know that falsey values and coercion means that == equality is NOT TRANSITIVE. For example ''==0 and 0=='0' but ''!='0'. This is relevant for Sets: I do not think one can override the notion of Set equality in a meaningful way. If one is using the built-in notion of Set equality (that is, ===), then the above should work. However if one uses a non-transitive notion of equality like ==, you open a can of worms: Even if you forced the user to define a hash function on the domain (hash(a)!=hash(b) implies a!=b) I’m not sure that would help… Certainly one could do the O(N^2) performance thing and remove pairs of == items one by one like a bubble sort, and then do a second O(N^2) pass to confirm things in equivalence classes are actually == to each other, and also != to everything not thus paired, but you’d STILL have to throw a runtime error if you have some coercion going on… You’d also maybe get weird (but potentially not that weird) edge cases with https://developer.mozilla.org/en-US/docs/Glossary/Falsy and Truthy values (with the exception that NaN==NaN… but just for Sets!). This is not an issue usually with most Sets of homogenous datatype.

    (sidenote: Maps are es6 dictionaries. I can’t tell if they have O(1) or O(log(N)) lookup performance, but in any case they are ‘ordered’ in the sense that they keep track of the order in which key-value pairs were inserted into them. However, the semantic of whether two Maps should be equal if elements were inserted in a different order into them is ambiguous. I give a sample implementation below of a deepEquals that considers two maps equal even if elements were inserted into them in a different order.)

    (note [1]: IMPORTANT: NOTION OF EQUALITY: You may want to override the noted line with a custom notion of equality, which you’ll also have to change in the other functions anywhere it appears. For example, do you or don’t you want NaN==NaN? By default this is not the case. There are even more weird things like 0==’0′. Do you consider two objects to be the same if and only if they are the same object in memory? See https://stackoverflow.com/a/5447170/711085 . You should document the notion of equality you use. )

    You should be able to extend the above to WeakMaps, WeakSets. Not sure if it makes sense to extend to DataViews. Should also be able to extend to RegExps probably, etc.

    As you extend it, you realize you do lots of unnecessary comparisons. This is where the type function that I defined way earlier (solution #2) can come in handy; then you can dispatch instantly. Whether that is worth the overhead of (possibly? not sure how it works under the hood) string representing the type is up to you. You can just then rewrite the dispatcher, i.e. the function deepEquals, to be something like:

    var dispatchTypeEquals = {
        number: function(a,b) {...a==b...},
        array: function(a,b) {...deepEquals(x,y)...},
        ...
    }
    function deepEquals(a,b) {
        var typeA = extractType(a);
        var typeB = extractType(a);
        return typeA==typeB && dispatchTypeEquals[typeA](a,b);
    }
    
    Reply
  2. For primitive values like numbers and strings this is an easy solution:

    a = [1,2,3]
    
    b = [3,2,1]
    
    a.sort().toString() == b.sort().toString() 
    

    The call to sort() will ensure that the order of the elements does not matter. The toString() call will create a string with the values comma separated so both strings can be tested for equality.

    Reply
  3. This method sucks, but I’ve left it here for reference so others avoid this path:


    Using Option 1 from @ninjagecko worked best for me:

    Array.prototype.equals = function(array) {
        return array instanceof Array && JSON.stringify(this) === JSON.stringify(array) ;
    }
    
    a = [1, [2, 3]]
    a.equals([[1, 2], 3]) // false
    a.equals([1, [2, 3]]) // true
    

    It will also handle the null and undefined case, since we’re adding this to the prototype of array and checking that the other argument is also an array.

    Reply
  4. jQuery does not have a method for comparing arrays. However the Underscore library (or the comparable Lodash library) does have such a method: isEqual, and it can handle a variety of other cases (like object literals) as well. To stick to the provided example:

    var a=[1,2,3];
    var b=[3,2,1];
    var c=new Array(1,2,3);
    
    alert(_.isEqual(a, b) + "|" + _.isEqual(b, c));
    

    By the way: Underscore has lots of other methods that jQuery is missing as well, so it’s a great complement to jQuery.

    EDIT: As has been pointed out in the comments, the above now only works if both arrays have their elements in the same order, ie.:

    _.isEqual([1,2,3], [1,2,3]); // true
    _.isEqual([1,2,3], [3,2,1]); // false
    

    Fortunately Javascript has a built in method for for solving this exact problem, sort:

    _.isEqual([1,2,3].sort(), [3,2,1].sort()); // true
    
    Reply
  5. Even if this would seem super simple, sometimes it’s really useful. If all you need is to see if two arrays have the same items and they are in the same order, try this:

    [1, 2, 3].toString() == [1, 2, 3].toString()
    true
    [1, 2, 3,].toString() == [1, 2, 3].toString()
    true
    [1,2,3].toString() == [1, 2, 3].toString()
    true
    

    However, this doesn’t work for mode advanced cases such as:

    [[1,2],[3]].toString() == [[1],[2,3]].toString()
    true
    

    It depends what you need.

    Reply
  6. This is what you should do. Please do not use stringify nor < >.

    function arraysEqual(a, b) {
      if (a === b) return true;
      if (a == null || b == null) return false;
      if (a.length !== b.length) return false;
    
      // If you don't care about the order of the elements inside
      // the array, you should sort both arrays here.
      // Please note that calling sort on an array will modify that array.
      // you might want to clone your array first.
    
      for (var i = 0; i < a.length; ++i) {
        if (a[i] !== b[i]) return false;
      }
      return true;
    }
    
    Reply
  7. With JavaScript version 1.6 it’s as easy as this:

    Array.prototype.equals = function( array ) {
      return this.length == array.length && 
             this.every( function(this_i,i) { return this_i == array[i] } )  
      }
    

    For example, [].equals([]) gives true, while [1,2,3].equals( [1,3,2] ) yields false.

    Reply
  8. Based on Tim James answer and Fox32’s comment, the following should check for nulls, with the assumption that two nulls are not equal.

    function arrays_equal(a,b) { return !!a && !!b && !(a<b || b<a); }
    
    > arrays_equal([1,2,3], [1,3,4])
    false
    > arrays_equal([1,2,3], [1,2,3])
    true
    > arrays_equal([1,3,4], [1,2,3])
    false
    > arrays_equal(null, [1,2,3])
    false
    > arrays_equal(null, null)
    false
    
    Reply
  9. It handle all possible stuff and even reference itself in structure of object. You can see the example at the end of code.

    var deepCompare = (function() {
        function internalDeepCompare (obj1, obj2, objects) {
            var i, objPair;
    
            if (obj1 === obj2) {
                return true;
            }
    
            i = objects.length;
            while (i--) {
                objPair = objects[i];
                if (  (objPair.obj1 === obj1 && objPair.obj2 === obj2) ||
                      (objPair.obj1 === obj2 && objPair.obj2 === obj1)  ) {                          
                    return true;
                }                    
            }
            objects.push({obj1: obj1, obj2: obj2});
    
            if (obj1 instanceof Array) {
                if (!(obj2 instanceof Array)) {
                    return false;
                }
    
                i = obj1.length;
    
                if (i !== obj2.length) {
                   return false; 
                }
    
                while (i--) {
                    if (!internalDeepCompare(obj1[i], obj2[i], objects)) {
                        return false;
                    }
                }
            }
            else {
                switch (typeof obj1) {
                    case "object":                
                        // deal with null
                        if (!(obj2 && obj1.constructor === obj2.constructor)) {
                            return false;
                        }
    
                        if (obj1 instanceof RegExp) {
                            if (!(obj2 instanceof RegExp && obj1.source === obj2.source)) {
                                return false;
                            }
                        }                 
                        else if (obj1 instanceof Date) {
                            if (!(obj2 instanceof Date && obj1.getTime() === obj2.getTime())) {
                                return false;
                            }
                        } 
                        else {    
                            for (i in obj1) {
                                if (obj1.hasOwnProperty(i)) {       
                                    if (!(obj2.hasOwnProperty(i) && internalDeepCompare(obj1[i], obj2[i], objects))) {
                                        return false;
                                    }
                                }
                            }         
                        }
                        break;
                    case "function": 
                        if (!(typeof obj2 === "function" && obj1+"" === obj2+"")) {
                            return false;
                        }
                        break;
                    default:                 //deal with NaN 
                        if (obj1 !== obj2 && obj1 === obj1 && obj2 === obj2) {
                            return false;            
                        }
                }
            }
    
            return true;
        }
    
        return function (obj1, obj2) {
            return internalDeepCompare(obj1, obj2, []);    
        };
    }());
    
    /*    
    var a = [a, undefined, new Date(10), /.+/, {a:2}, function(){}, Infinity, -Infinity, NaN, 0, -0, 1, [4,5], "1", "-1", "a", null],
        b = [b, undefined, new Date(10), /.+/, {a:2}, function(){}, Infinity, -Infinity, NaN, 0, -0, 1, [4,5], "1", "-1", "a", null];
    deepCompare(a, b);
    */
    
    Reply
  10. jQuery has such method for deep recursive comparison.

    A homegrown general purpose strict equality check could look as follows:

    function deepEquals(obj1, obj2, parents1, parents2) {
        "use strict";
        var i;
        // compare null and undefined
        if (obj1 === undefined || obj2 === undefined || 
            obj1 === null || obj2 === null) {
            return obj1 === obj2;
        }
    
        // compare primitives
        if (typeof (obj1) !== 'object' || typeof (obj2) !== 'object') {
            return obj1.valueOf() === obj2.valueOf();
        }
    
        // if objects are of different types or lengths they can't be equal
        if (obj1.constructor !== obj2.constructor || (obj1.length !== undefined && obj1.length !== obj2.length)) {
            return false;
        }
    
        // iterate the objects
        for (i in obj1) {
            // build the parents list for object on the left (obj1)
            if (parents1 === undefined) parents1 = [];
            if (obj1.constructor === Object) parents1.push(obj1);
            // build the parents list for object on the right (obj2)
            if (parents2 === undefined) parents2 = [];
            if (obj2.constructor === Object) parents2.push(obj2);
            // walk through object properties
            if (obj1.propertyIsEnumerable(i)) {
                if (obj2.propertyIsEnumerable(i)) {
                    // if object at i was met while going down here
                    // it's a self reference
                    if ((obj1[i].constructor === Object && parents1.indexOf(obj1[i]) >= 0) || (obj2[i].constructor === Object && parents2.indexOf(obj2[i]) >= 0)) {
                        if (obj1[i] !== obj2[i]) {
                            return false;
                        }
                        continue;
                    }
                    // it's not a self reference so we are here
                    if (!deepEquals(obj1[i], obj2[i], parents1, parents2)) {
                        return false;
                    }
                } else {
                    // obj2[i] does not exist
                    return false;
                }
            }
        }
        return true;
    };
    

    Tests:

    // message is displayed on failure
    // clean console === all tests passed
    function assertTrue(cond, msg) {
        if (!cond) {
            console.log(msg);
        }
    }
    
    var a = 'sdf',
        b = 'sdf';
    assertTrue(deepEquals(b, a), 'Strings are equal.');
    b = 'dfs';
    assertTrue(!deepEquals(b, a), 'Strings are not equal.');
    a = 9;
    b = 9;
    assertTrue(deepEquals(b, a), 'Numbers are equal.');
    b = 3;
    assertTrue(!deepEquals(b, a), 'Numbers are not equal.');
    a = false;
    b = false;
    assertTrue(deepEquals(b, a), 'Booleans are equal.');
    b = true;
    assertTrue(!deepEquals(b, a), 'Booleans are not equal.');
    a = null;
    assertTrue(!deepEquals(b, a), 'Boolean is not equal to null.');
    a = function () {
        return true;
    };
    assertTrue(deepEquals(
    [
        [1, 1, 1],
        [2, 'asdf', [1, a]],
        [3, {
            'a': 1.0
        },
        true]
    ], 
    [
        [1, 1, 1],
        [2, 'asdf', [1, a]],
        [3, {
            'a': 1.0
        },
        true]
    ]), 'Arrays are equal.');
    assertTrue(!deepEquals(
    [
        [1, 1, 1],
        [2, 'asdf', [1, a]],
        [3, {
            'a': 1.0
        },
        true]
    ],
    [
        [1, 1, 1],
        [2, 'asdf', [1, a]],
        [3, {
            'a': '1'
        },
        true]
    ]), 'Arrays are not equal.');
    a = {
        prop: 'val'
    };
    a.self = a;
    b = {
        prop: 'val'
    };
    b.self = a;
    assertTrue(deepEquals(b, a), 'Immediate self referencing objects are equal.');
    a.prop = 'shmal';
    assertTrue(!deepEquals(b, a), 'Immediate self referencing objects are not equal.');
    a = {
        prop: 'val',
        inside: {}
    };
    a.inside.self = a;
    b = {
        prop: 'val',
        inside: {}
    };
    b.inside.self = a;
    assertTrue(deepEquals(b, a), 'Deep self referencing objects are equal.');
    b.inside.self = b;
    assertTrue(!deepEquals(b, a), 'Deep self referencing objects are not equeal. Not the same instance.');
    b.inside.self = {foo: 'bar'};
    assertTrue(!deepEquals(b, a), 'Deep self referencing objects are not equal. Completely different object.');
    a = {};
    b = {};
    a.self = a;
    b.self = {};
    assertTrue(!deepEquals(b, a), 'Empty object and self reference of an empty object.');
    
    Reply
  11. There is no easy way to do this. I needed this as well, but wanted a function that can take any two variables and test for equality. That includes non-object values, objects, arrays and any level of nesting.

    In your question, you mention wanting to ignore the order of the values in an array. My solution doesn’t inherently do that, but you can achieve it by sorting the arrays before comparing for equality

    I also wanted the option of casting non-objects to strings so that [1,2]===[“1”,2]

    Since my project uses UnderscoreJs, I decided to make it a mixin rather than a standalone function.

    You can test it out on http://jsfiddle.net/nemesarial/T44W4/

    Here is my mxin:

    _.mixin({
      /**
      Tests for the equality of two variables
        valA: first variable
        valB: second variable
        stringifyStatics: cast non-objects to string so that "1"===1
      **/
      equal:function(valA,valB,stringifyStatics){
        stringifyStatics=!!stringifyStatics;
    
        //check for same type
        if(typeof(valA)!==typeof(valB)){
          if((_.isObject(valA) || _.isObject(valB))){
            return false;
          }
        }
    
        //test non-objects for equality
        if(!_.isObject(valA)){
          if(stringifyStatics){
            var valAs=''+valA;
            var valBs=''+valB;
            ret=(''+valA)===(''+valB);
          }else{
            ret=valA===valB;
          }
          return ret;
        }
    
        //test for length
        if(_.size(valA)!=_.size(valB)){
          return false;
        }
    
        //test for arrays first
        var isArr=_.isArray(valA);
    
        //test whether both are array or both object
        if(isArr!==_.isArray(valB)){
          return false;
        }
    
        var ret=true;
        if(isArr){
          //do test for arrays
          _.each(valA,function(val,idx,lst){
            if(!ret){return;}
            ret=ret && _.equal(val,valB[idx],stringifyStatics);
          });
        }else{
          //do test for objects
          _.each(valA,function(val,idx,lst){
            if(!ret){return;}
    
            //test for object member exists
            if(!_.has(valB,idx)){
              ret=false;
              return;
            }
    
            // test for member equality
            ret=ret && _.equal(val,valB[idx],stringifyStatics);
          });
    
        }
        return ret;
      }
    });
    

    This is how you use it:

    _.equal([1,2,3],[1,2,"3"],true)
    

    To demonstrate nesting, you can do this:

    _.equal(
        ['a',{b:'b',c:[{'someId':1},2]},[1,2,3]],
        ['a',{b:'b',c:[{'someId':"1"},2]},["1",'2',3]]
    ,true);
    
    Reply
  12. Using map() and reduce():

    function arraysEqual (a1, a2) {
        return a1 === a2 || (
            a1 !== null && a2 !== null &&
            a1.length === a2.length &&
            a1
                .map(function (val, idx) { return val === a2[idx]; })
                .reduce(function (prev, cur) { return prev && cur; }, true)
        );
    }
    
    Reply
  13. If you wish to check arrays of objects for equality and order does NOT matter, i.e.

    areEqual([{id: "0"}, {id: "1"}], [{id: "1"}, {id: "0"}]) // true

    you’ll want to sort the arrays first. lodash has all the tools you’ll need, by combining sortBy and isEqual:

    // arr1 & arr2: Arrays of objects 
    // sortProperty: the property of the object with which you want to sort
    // Note: ensure every object in both arrays has your chosen sortProperty
    // For example, arr1 = [{id: "v-test_id0"}, {id: "v-test_id1"}]
    // and          arr2 = [{id: "v-test_id1"}, {id: "v-test_id0"}]
    // sortProperty should be 'id'
    
    function areEqual (arr1, arr2, sortProperty) {
      return _.areEqual(_.sortBy(arr1, sortProperty), _.sortBy(arr2, sortProperty))
    }
    

    EDIT: Since sortBy returns a new array, there is no need to clone your arrays before sorting. The original arrays will not be mutated.

    Note that for lodash’s isEqual, order does matter. The above example will return false if sortBy is not applied to each array first.

    Reply
  14. Check every each value by a for loop once you checked the size of the array.

    function equalArray(a, b) {
        if (a.length === b.length) {
            for (var i = 0; i < a.length; i++) {
                if (a[i] !== b[i]) {
                    return false;
                }
            }
            return true;
        } else {
            return false;
        }
    }
    
    Reply
  15. If you are using lodash and don’t want to modify either array, you can use the function _.xor(). It compares the two arrays as sets and returns the set that contains their difference. If the length of this difference is zero, the two arrays are essentially equal:

    var a = [1, 2, 3];
    var b = [3, 2, 1];
    var c = new Array(1, 2, 3);
    _.xor(a, b).length === 0
    true
    _.xor(b, c).length === 0
    true
    
    Reply

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