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Partial application for login

importance: 5

The task is a little more complex variant of Ask losing this.

The user object was modified. Now instead of two functions loginOk/loginFail, it has a single function user.login(true/false).

What to pass askPassword in the code below, so that it calls user.login(true) as ok and user.login(fail) as fail?

function askPassword(ok, fail) {
  let password = prompt("Password?", '');
  if (password == "rockstar") ok();
  else fail();
}

let user = {
  name: 'John',

  login(result) {
    alert( this.name + (result ? ' logged in' : ' failed to log in') );
  }
};

askPassword(?, ?); // ?

Your changes should only modify the highlighted fragment.

  1. Either use a wrapper function, an arrow to be concise:

    askPassword(() => user.login(true), () => user.login(false));

    Now it gets user from outer variables and runs it the normal way.

  2. Or create a partial function from user.login that uses user as the context and has the correct first argument:

    askPassword(user.login.bind(user, true), user.login.bind(user, false));