Partial application for login
importance: 5
The task is a little more complex variant of Fix a function that loses "this".
The user object was modified. Now instead of two functions loginOk/loginFail, it has a single function user.login(true/false).
What should we pass askPassword in the code below, so that it calls user.login(true) as ok and user.login(false) 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.
-
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.
-
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));