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Identically equal and not identically equal

The operators also follow these rules when making comparisons:

Values of

null

and

undefined

are equal.

Values of

null

and

undefined

cannot be converted into any other values for equality checking.

If either operand is

NaN

, the equal operator returns

false

and the not equal operator returns

true

. Important note: Even if both operands are

NaN

, the equal operator returns

false

because,

by rule,

NaN

is not equal to

NaN

If both operands are objects, then the reference values are compared. If both operands point to

the same object, then the equal operator returns

true

. Otherwise, the two are not equal.

The following table lists some special cases and their results:

Expression

Value

null == undefined

true

“NaN” == NaN

false

5 == NaN

false

NaN == NaN

false

NaN != NaN

true

false == 0

true

true == 1

true

true == 2

false

undefined == 0

false

null == 0

false

“5” == 5

true

Identically equal and not identically equal

The brothers of the equal and not equal operators are the identically equal and not identically equal

operators. These two operators do the same thing as equal and not equal, except that they do not convert

operands before testing for equality. The identically equal operator is represented by three equal signs

(

===

) and only returns

true

if the operands are equal without conversion. For example:

var sNum = “55”;

var iNum = 55;

alert(sNum == iNum); //outputs “true”

alert(sNum === iNum); //outputs “false”

In this code, the first alert uses the equal operator to compare the string

“55”

and the number

and

outputs

“true”

. As mentioned previously, this happens because the string

“55”

is converted to the

number

and then compared with the other number

. The second alert uses the identically equal

ECMAScript Basics

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