Learning-JavaScript: when do we use"return"?

Hi! I am just a beginner in JavaScript and I am now learning Function. It kind of bothers me when I started to learn “return”, so I compare the following three functions, can someone explain why should we use “return” or why “return” is more advantageous? Thank you!!!

function monitorCount(rows, columns) {
return rows * columns;
}
const numOfMonitors = monitorCount(3,4);
console. log(numOfMonitors);//prints 12

function mCount(rows, columns) {
let area = rows * columns;
}
const a = mCount(3,4);
console. log(a);//prints undefined

function Count(rows, columns) {
console. log(rows * columns);
}
Count(3,4);//prints 12

Hi @jiehengwu0380423002 - welcome to the forum!

Essentially, you would use return whenever you need to “hand something back” to the code outside of your function.

If I borrow your examples…

function monitorCount(rows, columns) {
return rows * columns;
}
const numOfMonitors = monitorCount(3,4);
console. log(numOfMonitors);//prints 12

Here, what return rows * columns is doing is returning the value (12) to your variable numOfMonitors. From here, you can use that variable elsewhere in your code.

function mCount(rows, columns) {
let area = rows * columns;
}
const a = mCount(3,4);
console. log(a);//prints undefined

Here, you’re getting undefined because your function doesn’t return anything. As nothing comes back from mCount(3,4) to be assigned to const a, the constant remains undefined and JS tells you when you try to print it to the console.

function Count(rows, columns) {
console. log(rows * columns);
}
Count(3,4);//prints 12

Here, you get the output of 12 on the console because that’s what your function does. However, if we were to do

const b = Count(3,4)
console.log(b)

you would once again get undefined because we don’t return any value from the function.

So, if your function does something useful and you want to use its output elsewhere in your code you need a return to get that output into a variable. :slight_smile:

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Thank you for the detailed explanation!

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