Implicit Primitive Type Conversion Rule

Value

Converted to:

 

String

Number

Boolean

Object

undefined

"undefined"

NaN

false

throws TypeError

null

"null"

0

false

throws TypeError

true

"true"

1

True

new Boolean(true)

 

"false"

0

false

new Boolean(false)

"" (empty string)

 

0

false

new String("")

"1.2" (nonempty, numeric)

 

1.2

true

new String("1.2")

"one" (nonempty, non-numeric)

 

NaN

true

new String("one")

0

"0"

 

false

new Number(0)

-0

"0"

 

false

new Number(-0)

NaN

"NaN"

 

false

new Number(NaN)

Infinity

"Infinity"

 

true

new Number(Infinity)

-Infinity

"-Infinity"

 

true

new Number(-Infinity)

1 (finite, non-zero)

"1

 

true

new Number(1)

{} (any object)

see §3.8.3

see §3.8.3

true

 

[] (empty array)

""

0

true

 

[9] (1 numeric elt)

"9"

9

true

 

['a'] (any other array)

use join() method

NaN

true

 

function(){} (any function)

see §3.8.3

NaN

true