Why is 4 not an instance of Number?

Question

Just curious:

• 4 instanceof Number => false
• new Number(4) instanceof Number => true?

Why is this? Same with strings:

Answer 1

This is a nuance of Javascript which I've found catches some out. The instanceof of operator will always result in false if the LHS is not an object type.

Note that new String('Hello World') does not result in a string type but is an object. The new operator always results in an object. I see this sort of thing:

function fnX(value)
{
     if (typeof value == 'string')
     {
          //Do stuff
     }
}
fnX(new String('Hello World'));

The expectation is that "Do Stuff" will happen but it doesn't because the typeof the value is object.