The solution:

```js run demo
function delay(f, ms) {

  return function() {
    setTimeout(() => f.apply(this, arguments), ms);
  };

}

let f1000 = delay(alert, 1000);

f1000("test"); // shows "test" after 1000ms
```

Please note how an arrow function is used here. As we know, arrow functions do not have own `this` and `arguments`, so `f.apply(this, arguments)` takes `this` and `arguments` from the wrapper.

If we pass a regular function, `setTimeout` would call it without arguments and `this=window` (assuming we're in the browser).

We still can pass the right `this` by using an intermediate variable, but that's a little bit more cumbersome:

```js
function delay(f, ms) {

  return function(...args) {
    let savedThis = this; // store this into an intermediate variable
    setTimeout(function() {
      f.apply(savedThis, args); // use it here
    }, ms);
  };

}
```