What is the difference between “new Number(…)” and “Number(…)” in JavaScript?

Question

In Javascript, one of the reliable ways to convert a string to a number is the Number constructor:

var x = Number(\'09\'); // 9, because it defa         


        

Answer 1

Number returns a primitive number value. Yeah, it's a bit odd that you can use a constructor function as a plain function too, but that's just how JavaScript is defined. Most of the language built-in types have weird and inconsistent extra features like this thrown in.

new Number constructs an explicit boxed Number object. The difference:

typeof Number(1)      // number
typeof new Number(1)  // object

In contrast to Java's boxed primitive classes, in JavaScript explicit Number objects are of absolutely no use.

I wouldn't bother with either use of Number. If you want to be explicit, use parseFloat('09'); if you want to be terse, use +'09'; if you want to allow only integers, use parseInt('09', 10).