What's the difference between anonymous function and => notation in node.js?

Question

I just wanted to read a file with node.js.

I used to use this notation:

fs.readFile('/etc/passwd', function(err, data) {
  if (err) throw err;
  console.log(data);
});

Node.js’s documentation provides the following code:

fs.readFile('/etc/passwd', (err, data) => {
  if (err) throw err;
  console.log(data);
});

What's the difference between them?

score 6 · Accepted Answer · answered Feb 22 '16 at 22:12

6

Arrow functions have lexical this.

this.foo = 'bar';

baz(function() {
    this.foo // probably undefined
});

baz(() => {
    this.foo // == 'bar'
});

answered Feb 22 '16 at 22:12

josh3736

…and [more](http://stackoverflow.com/q/32535110/1048572) – Bergi Feb 22 '16 at 22:17
josh and the other ones answered my question more clearly. My question is a bit more specific about the difference of those two notations. If I would only know what a arrow function (a phrase I just learned from these answers here) is I wouldn't know that there is no (practical) difference (for me). – Dominik Feb 22 '16 at 22:31
yeah, if you don't need `this` for a method or `arguments.callee` (or `fn.name`) to do recursion, they are interchangeable. – dandavis Feb 22 '16 at 22:54

score 0 · Answer 2 · answered Feb 22 '16 at 22:12

0

=> is es6 notation. Arrow functions are ALWAYS anonymous. The two pieces of code you gave will function the same.

answered Feb 22 '16 at 22:12

UdaraW

score -4 · Answer 3 · answered Feb 22 '16 at 22:11

-4

The second is ECMA 6, the first is a bit older. There's no difference.

answered Feb 22 '16 at 22:11

djechlin

3 Answers3