Question

I am sure this is very simple but I can’t get seem to get this to work just right. Here is my code:

var zero = 10;

function some(elem, num) {
    return elem += num;
}

console.log(some(zero, 10));
console.log(some(zero, 10));
console.log(some(zero, 10));

From what I understand, I was expecting the variable in zero to increase each time by 10.. So, it would be 10, 20 and 30. Instead, I keep getting 10. Obviously, this isn’t right.

My question is, how would I increase the variable zero by 10 each time and save that value back to the variable zero?

Answer 1

JavaScript passes by value, so modifying the passed value won’t have any effect on the caller’s variable. You’d need to use the return value:

var zero = 10;

function sum(elem, num) {
    return elem + num;
}

console.log(zero = sum(zero, 10));
console.log(zero = sum(zero, 10));
console.log(zero = sum(zero, 10));