What does the plus sign do in '+new Date'

2018-06-04 02:43:39

I've seen this in a few places

function fn() {
    return +new Date;
}

And I can see that it is returning a timestamp rather than a date object, but I can't find any documentation on what the plus sign is doing.

Can anyone explain?

that's the + unary operator, it's equivalent to:

function(){ return Number(new Date); }

see: http://xkr.us/articles/javascript/unary-add/

and in MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators#Unary_plus

JavaScript is loosely typed, so it performs type coercion/conversion in certain circumstances:

http://blog.jeremymartin.name/2008/03/understanding-loose-typing-in.html
http://www.jibbering.com/faq/faq_notes/type_convert.html

Other examples:

>>> +new Date()
1224589625406
>>> +"3"
3
>>> +true
1
>>> 3 == "3"
true

Here is the specification regarding the "unary add" operator. Hope it helps...

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