==
is the abstract equality operator while ===
is the strict equality operator. The ==
operator will compare for equality after doing any necessary type conversions. The ===
operator will not do type conversion, so if two values are not the same type ===
will simply return false
. When using ==
, funky things can happen, such as:
1 == '1'; // true
1 == [1]; // true
1 == true; // true
0 == ''; // true
0 == '0'; // true
0 == false; // true
My advice is never to use the ==
operator, except for convenience when comparing against null
or undefined
, where a == null
will return true
if a
is null
or undefined
.
var a = null;
console.log(a == null); // true
console.log(a == undefined); // true