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

As stated in Christoph's answer, string and number literals are not the same as String and Number objects. If you use any of the String or Number methods on the literal, say

'a string literal'.length

The literal is temporarily converted to an object, the method is invoked and the object is discarded.
Literals have some distinct advantages over objects.

//false, two different objects with the same value
alert( new String('string') == new String('string') ); 

//true, identical literals
alert( 'string' == 'string' );

Always use literals to avoid unexpected behaviour!
You can use Number() and String() to typecast if you need to:

//true
alert( Number('5') === 5 )

//false
alert( '5' === 5 )