Return Ends the Function

return does two things at once: it gives a value back, and it ends the function immediately. The rest of the function doesn't run:

function add(a, b) {
    return a + b;
    console.log("This line never runs.");
}

console.log(add(2, 3));

This prints:

5

The line after return never runs, because the function ended one line earlier.

This is handy together with conditions. The following function describes the weather based on the temperature:

function describeWeather(degrees) {
    if (degrees < 0) {
        return "freezing";
    }
    if (degrees < 20) {
        return "cool";
    }
    return "warm";
}

console.log(describeWeather(-5));
console.log(describeWeather(12));
console.log(describeWeather(25));

This prints:

freezing
cool
warm

Let's follow the three calls:

• describeWeather(-5): -5 < 0 is true, so the function returns "freezing" and ends. The second condition is never checked.
• describeWeather(12): the first condition is false and the second one is true, so the function returns "cool".
• describeWeather(25): neither condition is true, so the function gets all the way to the last line and returns "warm".

We didn't need any else: once a return runs, the rest of the function is skipped anyway. But the order of the conditions matters, because the first return that runs wins. If the function checked degrees < 20 first, it would return "cool" for -5, since -5 is less than 20 too.