Earlier quoted context omitted.
That should work in the provided example, but in general `fn(cb)` is different: you lose the implied `this` binding unless you do `cb.bind(something)` beforehand. There's also some unexpected trouble due to potential extra parameters. Consider the output of ['1', '2', '3'].map(parseInt) gives: [1, NaN, NaN] So yea, fn(() => cb()) is the same as fn(() => {return cb()}) – just syntactic sugar when the anonymous functio…
I consider myself a pretty advanced JS developer, and I still don't understand how "this" works in JS. I avoid using it whenever I can.
Most common place IME you end up needing to use it are when assigning functions on a class as event listeners: if you want to be able to remove them, you need to use the same value in `addEventListener` as `removeEventListener`; and if the function uses other properties of the class, you must use `.bind(this)` to correctly set `this`.
It may help to think of it like this. This code
object.someFunction(a, b);
someFunction.call(object, a, b)
const fn = object.someFunction;
fn(a, b); // throw `this is undefined` error if function accesses this
const fn = object.someFunction.bind(object);
fn(a ,b);
// OR
fn.call(object, a, b);
class A {
a = 1;
fn() {
const thisRef = this;
return function () { return thisRef.a }
}
}
class A {
a = 1;
fn() {
return () => { return this.a }
}
}