What does the '+new' mean in JavaScript?

Question

Looking through the jQuery source in the function now() I see the following:

function now(){
    return +new Date;
}

I've never seen the plus operator prepended to the new operator like this. What does it do?

Answer 1

function now(){
    return +new Date;
}

This function means the developer is clever.

---

function now(){
    return (new Date()).getTime();
}

This function means, get the current time in milliseconds since 1970. And the developer has some mercy for those who wish to understand WTF is going on.

Answer 2

Nicolás and Brian are right, but if you're curious about how it works, +new Date(); is equivalent to (new Date()).valueOf();, because the unary + operator gets the value of its operand expression, and then converts it ToNumber.

You could add a valueOf method on any object and use the unary + operator to return a numeric representation of your object, e.g.:

var productX = {
  valueOf : function () {
    return 500; // some "meaningful" number
  }
};

var cost = +productX; // 500

Answer 3

I think the unary plus operator applied to anything would cause it to be converted into a number.

Answer 4

It converts the Date() into an integer, giving you the current number of milliseconds since January 1, 1970.