count++ != ++count

What is the result of this code?

let count = 0;
console.log(count++)

…it’s…

0

Let’s learn about post-increment and pre-increment

The pre-increment and pre-decrement operators increment (or decrement) their operand by 1, and the value of the expression is the resulting incremented (or decremented) value. The post-increment and post-decrement operators increase (or decrease) the value of their operand by 1, but the value of the expression is the operand’s value before the increment (or decrement) operation. - Wikipedia

Let’s look at what’s going on “under the hood”.

Here is a representation using a JavaScript class object.

postAdd = {count++} preAdd = {++count}

class Counter {
  constructor (){
    this.count = 0
  }
  postAdd(){
    let oldCount = this.count;
    this.count+=1;
    return oldCount
  }
  preAdd(){
    this.count += 1;
    return this.count
  }
}

let count = new Counter();

console.log(count.postAdd()) // 0

console.log(count.preAdd()) // 2 (the first console.log still increments!!!)

In my own words

{variable}++ can be used when you don’t reference the increased variable in that function call, and ++{variable} is valid when you need to reference the incremented variable immediately. -Zach Stone

Technically, pre increment is also faster since it is not creating a new variable each time.

How do you decide whether to use pre or post-increment?

Feel free to contact me using my website.

Have a fantastic day!