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Arrow functions' lexical binding is not working correctly #735
Description
The arrow function is supposed to bind to the scope in which it is defined (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions), and the this of an arrow function should not be able to change. As shown in the code below (run with the --harmony_arrow_functions), the arrow functions are not correctly binding.
var obj = {
init: function() {
this.handle(this.cb);
},
cb: val => {
console.log(this.val);
console.log(val);
return val + this.val;
},
handle: function(cb) {
console.log(cb(3));
},
val: 5
};
console.log('calling cb directly');
console.log(obj.cb(3));
// 5
// 3
// 8
console.log('calling cb via init');
obj.init();
// undefined
// 3
// NaN
Activity
phpnode commentedon Feb 5, 2015
@smfoote this is a V8 bug, the arrow function implementation in the current V8 is not spec compliant and shouldn't be used. If you want/need such features, you'll have to use something like 6to5 for now.
bnoordhuis commentedon Feb 5, 2015
@smfoote A general observation: if you have to pass a flag to enable a language feature in V8, the feature isn't stable yet.
smfoote commentedon Feb 6, 2015
Thanks, all. I was simply trying to help by pointing out that the feature is not yet up to spec. I won't submit any other issues for features hidden by flags.
bnoordhuis commentedon Feb 6, 2015
@smfoote That's appreciated. :-) Most things V8 are not under our direct control, though.