CODEWITHSUNDEEP
javascriptarraysequality
Ye Lin Aung
Ye Lin Aung

Reputation: 11459

Javascript Comparision expression

I am confused about javascript comparison. let's say :

var array1 = [1,2,3];
var array2 = [1,2,3];

array1 == array2 ; 
false // why false ? 

array1 === array2;
false // also why false?

Can anyone explain this to me clearly? Thank you in advance.

Upvotes: 2

Views: 331

Answers (2)

user113716
user113716

Reputation: 322492

They are false because you are comparing two different Array instances. It will only be true if they are actually references to the same instance.

var array1 = [1,2,3];
var array2 = array1;

array1 == array2 ; // true

To compare their content, you need to compare each item individually. Something like this, though this doesn't look any deeper than the one level.

var array1 = [1,2,3];
var array2 = [1,2,3];

function compareArrays(a1,a2) { 
    var len = a1.length;
    if( len !== a2.length )
        return false;
    while( len-- ) {
        if( a1[ len ] !== a2[ len ] ) {
            return false;
        }
    }
    return true;
}

compareArrays( array1, array2 ); // true

Upvotes: 4

Adam
Adam

Reputation: 44929

"Objects, arrays, and functions are compared by reference."

-- O'Reilly's JavaScript: The Definitive Guide

In your case array1 is a reference to a different Array than array2.

See here for a way to compare Arrays.

Upvotes: 4

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