The Difference Between i++ and ++i (Postfix vs. Prefix)

This post was originally published at kais.blog.

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JavaScript (and many other languages) support the postfix and the prefix increment operator (++). You have probably seen and used it before.

Often it's used like this:

i++;

In this case it's almost equivalent to:

i = i + 1;

But, what do you think? Is there a difference between

let i = 3;
const j = i++;

and

let i = 3;
const j = ++i;

...

Well, yes. The first example uses the postfix increment operator (i++). The second example uses the prefix increment operator (++i). At first, it seems like there's no difference. However, it's important to understand what is going on here:

The postfix increment operator increments the value and returns the value before the increment.

The prefix increment operator increments the value and returns the value after the increment.

Let's take a look at our two examples again:

// postfix increment

let i = 3;
const j = i++;

console.log({ i, j }); // { i: 4, j: 3 }

// prefix increment

let i = 3;
const j = ++i;

console.log({ i, j }); // { i: 4, j: 4 }

Spotted the difference? The value of j differs. Therefore, it is important to know this small difference between postfix and prefix.

By the way, the same applies to the postfix decrement and prefix decrement operator (--). The only difference is, that instead of incrementing we are decrementing the value.

That's all there is to say. I hope I made the difference a bit clearer. See you soon!

Let's move your learning forward together! Follow me on Twitter for your daily dose of developer tips. Thanks for reading my content!

This post was originally published at kais.blog.