Why 3 equal symbols in boolean comparisons?

Answer 1

The === does not allow type coercion, so something like this would return false:

if (2 === '2') // false

The "normal" javascript == operator does allow type coercion, and so this would return true:

if (2 == '2') // true

Answer 2

Checks that the type as well as the values match. This is important since (0 == false) is true but (0 === false) is not true.

Answer 3

var a = 3;
var b = "3";

if (a == b) {
  // this is true.
}

if (a === b) {
  // this is false.
}

Answer 4

=== is typically referred to as the identity operator. Values being compared must be of the same type and value to be considered equal. == is typically referred to as the equality operator and performs type coercion to check equality.

An example

1 == '1' // returns true even though one is a number, the other a string

1 === '1' // returns false. different datatypes

Doug Crockford touches briefly on this in JavaScript the Good Parts google tech talk video. Worth spending an hour to watch.