Naming arrow functions

[jscriptcoder]

Hi there,

Not sure whether this has been already mentioned before (I would be surpirsed if it never was)... Wouldn't it be a good idea to name arrow functions, which is what apparently ES6 does?. Think about the benefits of this in the stacktrace. It's quite useful to have a "named" function in there, instead of an anonymous one ;-)

So, this:

const double = x => x * 2;

would be transpiled down to:

var double = function double(x) {
  return x * 2;
};

Just to mention that Babel does it like that ;-)

Thanks.

[adidahiya]

This would also be nice to have for arrow functions used as class methods/properties.

private handleDocumentClick = (...) => {
    ...
}

[RyanCavanaugh]

Wouldn't it be a good idea to name arrow functions, which is what apparently ES6 does?

Can you clarify this part?

[RyanCavanaugh]

This would also be nice to have for arrow functions used as class methods/properties.

Note that we can't safely name class methods -- a reference to handleDocumentClick in the method body must refer to whatever that name means in the enclosing lexical scope, not the function itself.

[RyanCavanaugh]

Consulted with @bterlson and we think this is a spec-affecting behavior, specifically the places where the abstract SetFunctionName operation is invoked https://tc39.github.io/ecma262/#sec-setfunctionname

Regular function expressions have very noncomplaint behavior in current runtimes and should probably just be left alone (specifically, Edge, Chrome, and Node all produce an own property of name on functions, when they shouldn't)

[jscriptcoder]

Hi @RyanCavanaugh, answering your question... as far as I know in ES6 if an arrow function is defined on the right-hand-side of an assignment expression, the ‎engine will take the name on the left-hand-side and set the arrow function's ".name" based on that

Thanks

[nojvek]

Hi @RyanCavanaugh, could you explain the SetFunctionName operation? I couldn't fully grasp why it should be an issue.

I tried this in chrome.

let l = {log(){}}
console.log(l.log.name) //outputs 'log'

Generated typescript:

var l = { log: function () { } };
l.log.name // empty

So it seems under the covers v8 makes nice named anonymous functions.

[basarat]

Tried the following in the chrome dev console. Was surprised 🌹

let foo = function(){}
foo.name; // "foo"

[dsherret]

@basarat It didn't happen for me in v50.0.2661.102m, but I just upgraded to v51.0.2704.63m and now it's doing that.