← Back tothis vs that

++value vs value++

Written byPhuoc Nguyen
Category
JavaScript
Created
15 Jul, 2020
Last updated
22 Aug, 2022
Contributors
joshuadelange
`++` is the increment operator adding one to the operand. There're two variables of the operator which use `++` as prefix or postfix: `++value` and `value++`.
They have the same effect in for loops. The following loops print the same results which are the numbers from 0 to 4:
for (let i = 0; i < 5; i++) {
console.log(i);
}

// And
for (let i = 0; i < 5; ++i) {
console.log(i);
}

Differences

When returning a value, `return value++` returns the original value before the value is increased. While `return ++value` increases the value and returns the updated value.
The following `foo` and `bar` functions returns different results:
const foo = (x) => x++;
const bar = (x) => ++x;

foo(1); // 1
bar(1); // 2

Good to know

`value += 1` is another alternative of the postfix increment `value++`. It's worth noting that they can provide different result when using with strings.
The postfix increment `value++` will convert the value to number first, and then increase the value:
let value = '5';
value++;
value; // 6
On the other hand, if value is a string, `value += 1` converts the second argument (`1`) to string first, and then concatenate them together.
let value = '5';
value += 1;
value; // '51'

Questions? 🙋

Do you have any questions? Not just about this specific post, but about any topic in front-end development that you'd like to learn more about? If so, feel free to send me a message on Twitter or send me an email. You can find them at the bottom of this page.
I have a long list of upcoming posts, but your questions or ideas for the next one will be my top priority. Let's learn together! Sharing knowledge is the best way to grow 🥷.

Recent posts ⚡

Newsletter 🔔

If you're into front-end technologies and you want to see more of the content I'm creating, then you might want to consider subscribing to my newsletter.
By subscribing, you'll be the first to know about new articles, products, and exclusive promotions.
Don't worry, I won't spam you. And if you ever change your mind, you can unsubscribe at any time.
Phước Nguyễn