object - Why does ("foo" === new String("foo")) evaluate to false in JavaScript? -

i going start using === (triple equals, strict comparison) time when comparing string values, find

"foo" === new string("foo")

is false, , same this:

var f = "foo", g = new string("foo"); f === g; // false

of course:

f == g; // true

so recommended use == string comparison, or convert variables strings before comparing?

"foo" string primitive. (this concept not exist in c# or java)

new string("foo") boxed string object.

the === operator behaves differently on primitives , objects.
when comparing primitives (of same type), === return true if both have same value.

when comparing objects, === return true if refer same object (comparing reference). thus, new string("a") !== new string("a").

in case, === returns false because operands of different types (one primitive , other object).

primitives not objects @ all.
typeof operator not return "object" primitives.

when try access property of primitive (using object), javascript language box object, creating new object every time. described in specification.

this why cannot put properties on primitives:

var x = "a"; x.property = 2; alert(x.property) //undefined

each time write x.property, different boxed string object created.

EXC