I have two arrays say a = [1,2,3] and b=[1,2,3]

if i do (a==b) it returns false. how to compare two arrays with same values?

a[0]==b[0] will return true, but how can we compare two arrays instead of 2 same elements inside two different arrays?

I have two arrays say a = [1,2,3] and b=[1,2,3]

if i do (a==b) it returns false. how to compare two arrays with same values?

a[0]==b[0] will return true, but how can we compare two arrays instead of 2 same elements inside two different arrays?

• javascript
• arrays

• 1 You have to write the code to loop through all the elements. – Pointy Commented Sep 13, 2012 at 18:19
• @Pointy usually i do that. but just wanted to know is there any way other than looping? – Shreedhar Commented Sep 13, 2012 at 18:20
• 1 No, there is no built-in array comparison facility in JavaScript. – Pointy Commented Sep 13, 2012 at 18:20

8 Answers 8

function array_compare(a, b)
{
    // if lengths are different, arrays aren't equal
    if(a.length != b.length)
       return false;

    for(i = 0; i < a.length; i++)
       if(a[i] != b[i])
          return false;

    return true;
}

You have 2 options.

Fisrt one is to use some kind of function made by yourself that will iterate over each key from both arrays and compare them.

Second option is to use isEqual from _.underscore (a really nice JS library, http://underscorejs.org/#isEqual ) This will work for both arrays and objects.

I'd use the second one as it's easier.

var a = {'a' : '1', 'b' : '2', 'c' : '3'};
var b = {'a' : '1', 'b' : '2', 'c' : '3'};
_.isEqual(a, b) // --> true

Note that order doesn't matter in objects, so you could have

var a = {'a' : '1', 'b' : '2', 'c' : '3'};
var b = {'c' : '3', 'b' : '2', 'a' : '1'}
_.isEqual(a, b) // --> also true

If you know what (not) to expect in your array you could use join:

a.join() == b.join()

I know, this is far from bulletproof, but it can be usable some cases (when you know the order in both arrays will be the same).

If you want to compare 2 arrays, you could use JSON.stringify

JSON.stringify([1,2,3]) === JSON.stringify([1,2,3]); //=> true

It will also compare [nested] Objects within the array, or [nested] Arrays within an Array:

JSON.stringify([1,2,3,{a:1,b:2}]) === 
  JSON.stringify([1,2,3,{'a':1,b:2}]); //=> true

JSON.stringify([1,2,3,{a:1,b:2,c:{a:1,b:2}}]) === 
  JSON.stringify([1,2,3,{'a':1,b:2,c:{a:1,b:2}}]); //=> true

JSON.stringify([1,2,3,{a:1,b:2,c:[4,5,6,[7,8,9]]}]) === 
  JSON.stringify([1,2,3,{'a':1,b:2,c:[4,5,6,[7,8,9]]}]); //=> true

In this jsfiddle, I've played a bit with the idea

(a==b) is doing a reference comparaison not a content comparaison.

Underscore.js brings some feature for that.

You must write code to compare each element of an array to accomplish your objective.

// this is one way of doing it, and there are caveats about using instanceOf. 
// Its just one example, and presumes primitive types.
function areArrayElementsEqual(a1, a2)
{
    if (a1 instanceof Array) && (a2 instanceof Array)
    {
        if (a1.length!=a2.length)
            return false;
        else{
           var x;
           for (x=0;x<a1.length; x++)
              if (a1[x]!=a2[x])
                 return false;
        }
    }

    return true;

}

Try using javascripts Join() method to convert the two arrays to strings and then compage the strings:

Join(): The string conversions of all array elements are joined into one string.

var a1 = array1.join();
var a2 = array2.join();

if(a1 == a2){
  //do something
}

It's the shortest way I found:

""+ar1==""+ar2

Fiddle