When to use return, and what happens to returned data?

Question

What is the difference between:

function bla1(x){console.log(x)}

and

function bla(x){return console.log(x)}

I

Answer 1

With return you specify what the value of a function is. You can use this value to do further operations or to store it into a variable and so on.

Since console.log returns undefined, the examples in your question are equivalent, as a function not reaching a return statement will return undefined as well. But let me give you an example:

function sum(arr) {
    var s = 0;
    for (var index in arr) {
        s += arr[index];
    }
    return s;
}

function prodsum(arr, scalar) {
    return scalar * sum(arr);
}

console.log(prodsum([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3));

The result will be 165. If we remove the returns, then both functions will return undefined:

function sum(arr) {
    var s = 0;
    for (var index in arr) {
        s += arr[index];
    }
    s;
}

function prodsum(arr, scalar) {
    scalar * sum(arr);
}

console.log(prodsum([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3));

and the result will be undefined as well. Basically, if you want the function to have a conclusion or final value, then you have a return in it.