How does function.apply.bind work in the following code?

Question

So I get that an array of [200,599] is returned from the promise and the callback function inside spread is being passed into Function.apply.bind, but now I\'m lost. How is

Answer 1

.apply() is a method on function objects. Like so:

console.log(Math.max.apply(null, [1, 2, 3])); // 3

.apply() accepts two arguments, the context (what would become this inside of the target function) and an iterable of arguments (usually an array, but the arguments array like also works).

---

.bind() is a method on function objects. Like so:

const x = {
  foo: function() {
    console.log(this.x);
  },
  x: 42
}

var myFoo = x.foo.bind({x: 5});

x.foo(); // 42
myFoo(); // 5

.bind() takes a context (what would become this), and optionally, additional arguments, and returns a new function, with the context bound, and the additional arguments locked

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Since .apply() is a function in on itself, it can be bound with .bind(), like so:

Function.prototype.apply.bind(fn, null);

Meaning that the this of .apply() would be fn and the first argument to .apply() would be null. Meaning that it would look like this:

fn.apply(null, args)

Which would spread the parameters from an array.