Why doesn't my code work right? Can you please explain what I did wrong?

Question

I can receive the right output in the console, but can't return the value:

function getNum(num, cb) {
setTimeout(() => cb(num), 1000);
}

function plusTen(num) {
return getNum(num, (arg) => {
console.log(`result: ${arg + 10}`); //output: result: 15
return arg + 10; // nothing
});
}

console.log(plusTen(5)); // undefined

Answer 1

getNum doesn't return anything, that's why the output is undefined.
Adding a return statement to this function won't help you, because setTimeout returns timer id.

You can either pass a callback to the calling function like this:
plusTen(5, (getNumResult) => doSomethingWithResult);

and then call it instead of "return arg +10":
cb(arg + 10)

... or you can use Promises.