Javascript Double Equals vs Triple Equals Comparison Operator

• Javascript Double Equals vs Triple Equals Comparison Operator
• Double Equals vs Triple Equals Comparison Example #1
• Double Equals vs Triple Equals Comparison Example #2

Javascript Double Equals vs Triple Equals Comparison Operator

The identity (===) operator behaves identically to the equality (==) operator except no type conversion is done, and the types must be the same to be considered equal.

The == operator will compare for equality after doing any necessary type conversions. The === operator will not do the conversion, so if two values are not the same type === will simply return false. Both are equally quick.

If the two operands are of the same type and have the same value, then === produces true and !== produces false. The double == and != do the same thing when the operands are of the same type, but if they are of different types, they attempt to coerce the values.

Example 1

1919 === '1919'

0 == false
0 === false

"" == false
"" === false

Following are some of the interesting cases:

Example 2

var a = [1,2,3];
var b = [1,2,3];

var c = { x: 1, y: 2 };
var d = { x: 1, y: 2 };

var e = "text";
var f = "te" + "xt";

a == b            // false
a === b           // false

c == d            // false
c === d           // false

e == f            // true
e === f           // true

The special case is when you compare a literal with an object that evaluates to the same literal, due to its toString or valueOf method. For example, consider the comparison of a string literal with a string object created by the String constructor.

"abc" == new String("abc")    // true
"abc" === new String("abc")   // false

Here the == operator is checking the values of the two objects and returning true, but the === is seeing that they’re not the same type and returning false. Which one is correct? That really depends on what you’re trying to compare.

Reference: http://www.ecma-international.org