ECMA Script 6 Arrow functions as object properties

Question

I realise this is a pointless thing to do but I don't understand why it doesn't work.

var person = {
    _name: "Steve",
    doSomething: () => console.debug("Doing stuff with ", this._name)
}

"this" is bound to the global object and not the object getName was invoked on. I was expecting that the above is equivalent to :

var person = {
    _name: "Steve",
    doSomething: function() { console.debug("Doing stuff with ", this._name) }
}

(I know you should write it like this)

var person = {
   _name: "Steve",
   doSomething() {
      console.debug("Doing stuff with ", this._name)
   }
}

"I know you should write it like this" - No, you should not. — thefourtheye
– thefourtheye, Commented Oct 23, 2014 at 11:47
Strange: In Chrome Version 38.0.2125.104 (64-bit), this still refers the window object. — thefourtheye
– thefourtheye, Commented Oct 23, 2014 at 12:00
@thefourtheye sure you're calling it like person.getName()? — simonzack
– simonzack, Commented Oct 23, 2014 at 12:00
@thefourtheye I cannot think why you say you should not use that style - perhaps I confused the issue by using a get function, suppose the function does something other that simply return a value. developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Woody
– Woody, Commented Oct 23, 2014 at 12:08
And I guess, the equivalent would rather be function() { return console.debug("Doing stuff with ", this._name) } — Liglo App
– Liglo App, Commented Dec 18, 2014 at 11:35

simonzack · Accepted Answer · 2014-10-23 12:16:56Z

1

From mdn:

Arrow functions capture the this value of the enclosing context

This is different to functions.

answered Oct 23, 2014 at 11:49

simonzack

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3 Comments

@RahilWazir Oh, I didn't see the class, I thought that it is a function.

@Woody Hmm I thought that part got nuked from ES6, it was probably something else, I've removed that part from my answer.