Functions and Arrays

An argument can be any value, an array too. A function that gets an array can go through it with a loop and return a result. This function adds up all the numbers in an array:

function sum(numbers) {
    let total = 0;
    for (const number of numbers) {
        total += number;
    }
    return total;
}

console.log(sum([1, 2, 3]));

const prices = [120, 45, 80];
console.log(sum(prices));

This prints:

6
245

The parameter numbers holds whatever array the call passes: first [1, 2, 3], then the array prices. You know the loop from the lesson on loops, but now it's inside a function, so you can add up any array with a single line. And because total is a local variable, every call starts from 0 again.

Notice where the return is: after the loop, when all the numbers have been added up. A common mistake is to put it inside the loop:

function sum(numbers) {
    let total = 0;
    for (const number of numbers) {
        total += number;
        return total;
    }
}

console.log(sum([1, 2, 3]));

This prints:

1

return ends the whole function, and the loop with it, already in the first iteration. So the function returns just the first number.