How can I check if arrays are equal in javascript?

Question

Have a look at this code sample or go to the jsfiddle

function printRelation(a, b, out) {
    var text;
    if (a === b) {
        text = "a === b";
    } else if (a == b) {
        text = "a == b";
    } else {
        text = "a != b";
    }
    $('#' + out).text(text);
}

var a = [0, 0, 2], b = a;
printRelation(a, b, 'out1');
a = [0, 0, 2];
b = [0, 0, 2];
printRelation(a, b, 'out2');

I would have expected both tests to output a === b, but only the first one does. The second one outputs a != b. Can anyone explain this behaviour? How can I efficiently compare arrays in javascript?

Answer 1

You can use the Underscore.js library's isEqual method.

http://underscorejs.org/#isEqual

Performs an optimized deep comparison between the two objects, to determine if they should be considered equal.

var moe   = {name : 'moe', luckyNumbers : [13, 27, 34]};
var clone = {name : 'moe', luckyNumbers : [13, 27, 34]};
moe == clone;
=> false
_.isEqual(moe, clone);
=> true

---

UPDATE

Lodash is inspired by underscore, but nowadays is superior solution

https://lodash.com/docs/#isEqual

Performs an optimized deep comparison between the two objects, to determine if they should be considered equal.

var object = { 'a': 1 };
var other = { 'a': 1 };

_.isEqual(object, other);
// => true

object === other;
// => false