Partial application for login
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 usesuser
as the context and has the correct first argument:askPassword(user.login.bind(user, true), user.login.bind(user, false));