What does the colon operator do in this context?

Question

I was looking at piece of code on How to subtract date/time in javascript? which is like

Date.prototype.diffDays = function (date: Date): number {

    var utcThis = Date.UTC(this.getFullYear(), this.getMonth(), this.getDate(), this.getHours(), this.getMinutes(), this.getSeconds(), this.getMilliseconds());
    var utcOther = Date.UTC(date.getFullYear(), date.getMonth(), date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds(), date.getMilliseconds());

    return (utcThis - utcOther) / 86400000;
};

and I'm wondering what the (date: Date): number means since I've never seen anything like that and I know this isn't like ECA6 or whatever since the post was made in 2011

This syntax also appears in ActionScript, also an ECMAScript derivative. — BoltClock, Jan 06 '16 at 17:40
@torazaburo The OP found it in [this answer](http://stackoverflow.com/a/14779469/2680216) (as stated in the question). — Josh Crozier, Jan 06 '16 at 17:50

score 3 · Answer 1 · answered Jan 06 '16 at 17:37

3

That's TypeScript. It's a function that accepts a parameter of type date and returns a number

answered Jan 06 '16 at 17:37

Brian

3,701
16
26

score 3 · Answer 2 · answered Jan 06 '16 at 17:38

3

This is typescript (http://www.typescriptlang.org/), a superset of javascript that adds typing to variables, not pure javascript.

answered Jan 06 '16 at 17:38

BiAiB

11,493
7
40
59

What does the colon operator do in this context?

2 Answers2