Yeesh, it's a long article for a simple thing. They just let you control the implicit this arg to a function call.

fn.call(t, x, y, ...) calls fn(x, y, ...) with t as this.

fn.apply(t, args) is fn.call(t, ...args).

fn.bind(t, x, y, ...) is (...args) => fn.call(t, x, y, ..., ...args).