What does `=>` do in Mozilla's JavaScript?

Question

In Mozilla's sample code for Downloads.jsm there's a few lines that use => which I don't know the meaning of:

let view = {
  onDownloadAdded: download => console.log("Added", download),
  onDownloadChanged: download => console.log("Changed", download),
  onDownloadRemoved: download => console.log("Removed", download),
};

What does => do here?

possible duplicate of [What's the meaning of “=>” in JavaScript?](http://stackoverflow.com/q/24900875/1048572) — Bergi, Dec 17 '15 at 18:12

score 3 · Answer 1 · answered Dec 20 '13 at 05:39

3

They're a special function literal notation, called arrow functions, introduced with ES6. It's basically the same as in coffeescript.

It could have been shorter written as console.bind(console, "Added") :-)

answered Dec 20 '13 at 05:39

Bergi

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score 2 · Accepted Answer · answered Dec 20 '13 at 05:40

2

It's the syntax of upcoming version of JavaSctipt, the ECMAScript 6, aka Harmony.

The x => expr syntax stands, more or less (with differences with treatment of this), for function (x) { return expr; }.

answered Dec 20 '13 at 05:40

score 1 · Answer 3 · answered Dec 20 '13 at 05:52

That is called "arrow functions" or "lambda expressions".

If you want to use that and not wait for ECMAScript 6, you can have a look at typescript , you don't have to worry about browser compatibility and this kind of stuff.

You can check an example here.

What does `=>` do in Mozilla's JavaScript?

3 Answers3