JavaScript: Function.prototype.call

f.call(obj)

Call f with its this Binding having value of obj.

f.call(obj, arg1, arg2 etc)

Feed f with arguments arg1, arg2 etc.

// shows what f.call(arg) is doing

function ff() { return this; }

const obj = {};

console.log(
 ff.call(obj) === obj
); // true

Example with arguments.

function ff(a, b) { return a + b; }

console.log(
 ff.call(undefined, 3, 4) === 7
);
// true

Reflect.apply

Tip: better to use Reflect.apply