CoffeeScript, What is the difference between => and ->

Question

I am new to CoffeeScript. I have run into this today.

example -> 
 a ->

and

example ->
 b =>

What this the different between a thin arrow vs a fat arrow?

Could someone please explain the difference and when they should be used.

This question appears to be off-topic because it is about not reading the documentation. — rlemon, Sep 30 '13 at 16:36
@ rlemon I do not feel it is off topic, I was reading the documentation and did not understand. — Tyler, Sep 30 '13 at 16:38

score 12 · Accepted Answer · answered Sep 30 '13 at 16:30

12

The fat arrow => defines a function bound to the current value of this.

This is handy especially for callbacks.

Notice the generated differences

Coffee script:

foo = () -> this.x + this.x;
bar = () => this.x + this.x;

JavaScript

var bar, foo,
  _this = this;

foo = function() {
  return this.x + this.x;
};

bar = function() {
  return _this.x + _this.x;
};

answered Sep 30 '13 at 16:30

Daniel A. White

2

what is the difference between _this and this? – Tyler Sep 30 '13 at 16:36
@Tyler `_this` is just a variable name. `this` is a language keyword (in JS, think of @ in CS) – Benjamin Gruenbaum Sep 30 '13 at 16:37
ok I know what this means I was just unclear on _this – Tyler Sep 30 '13 at 16:39
1

@Tyler - javascript binds events and functions to the caller - so `this` might not be your object. – Daniel A. White Sep 30 '13 at 16:47

1 Answers1