• NaN is not equal to anything including itself.
• Negative zero equals positive zero.
• null equals both null and undefined.

Every other comparison is considered unequal. JavaScript's identity (strict equality) operators (=== and !==) behave identically to the equality operators except no type conversion is done, and the types must be the same to be considered equal. Here are a few examples:

"3" == 3 // true
"3" === 3 // false
1 == true // true
1 === true // false
"1" == true // true
"1" === true // false

The problem with JavaScript's identity operators is that they are only supported by some browsers:

Browser:	IE4	IE5	N2	N3	N4/C4 (JS1.2)	N4.06/C4.5 (JS1.3)
Type Conversion (== and !=)	yes	yes	yes	yes	no	yes
Available (=== and !==)	yes	yes	no	no	no	yes

IE = Microsoft Internet Explorer
N = Netscape Navigator (standalone)
C = Netscape Communicator

We can use the typeof operator to achieve the same results:

function seq(x, y) { // ===
  return ((typeof(x) == typeof(y)) && (x == y)); // AND
}

function sneq(x, y) { // ===
  return ((typeof(x) != typeof(y)) || (x != y)); // OR
}

seq("3", 3) // false
sneq("3", 3) // true
seq(1, true) // false
sneq(1, true) // true
seq("1", true) // false
sneq("1", true) // true
seq(5, 5) // true
sneq(5, 5) // false

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