What is the difference between == and === in JavaScript?

Double equals (==) is abstract equality comparison operator, which transforms the operands to the same type before making the comparison. 

For example,

4    ==  4        // true '4'  ==  4        //true 4    == '4'       // true 0    == false     // true

Triple equals (===) are strict equality comparison operator, which returns false for different types and different content.

For example,

4 === 4  // true 4 === '4' // false var v1 = {'value':'key'}; var v2 = {'value': 'key'}; v1 === v2 //false