What is this JavaScript parameter syntax called?

Question

I've seen a few JavaScript code examples that use this sort of syntax:

function(foo:String) {
  // code
}

I assume it does some sort of typecasting, but haven't been able to find much information about this syntax. Does anyone know what this is called, and where it is documented? Is this strict JavaScript or a browser extension?

It's popped up mostly in dumb little sample bits on LifeHacker. I was googling for TextMate themes and came across screenshots. Could very well be ActionScript as BoltClock suggests, though in the editor "JavaScript" is selected for syntax highlighting. — Eric
– Eric, Commented Oct 25, 2011 at 14:59
Here's a link: lifehacker.com/5817833/the-best-programming-text-editor-for-mac — Eric
– Eric, Commented Oct 25, 2011 at 15:00

BoltClock · Accepted Answer · 2011-10-25 15:02:44Z

5

As far as I know, that's not valid JavaScript. Rather, it's ActionScript (with both languages being based on the ECMAScript standard). It simply tells the compiler that the parameter's type is String or any of its subclasses.

This declaration is covered in Adobe's AS3 documentation for variables. The same syntax is used for local variables, fields, function parameters and function return types.

edited Oct 25, 2011 at 15:02

answered Oct 25, 2011 at 14:54

BoltClock

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3 Comments

James Johnson Over a year ago

Ah, thank God! I was beginning to wonder if I had a huge gap in my knowledge of JavaScript!

Eric Over a year ago

That would make a LOT of sense. I saw this in this screenshot and assumed it was JavaScript: lifehacker.com/5817833/the-best-programming-text-editor-for-mac

Eric Over a year ago

@JamesJohnson, I was similarly terrified.

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