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# Understanding increment / decrement PREFIX or POSTPREFIX operator

March 28, 20201 MIN READ

Key:

Increment or Decrement operator can appear in two forms, the POSTPREFIX `x++ or x--`

and PREFIX `++x or --x`

and it can be quite confusing.

Understanding how both works will enable you know how to apply them in your project.

**POSTPREFIX**

This returns the value of its operand **BEFORE** adding 1 to it - **Increment**

This returns the value of its operand **BEFORE** subtracting 1 from it - **Decrement**

```
// increment
let x = 2
const r1 = x++ = 2 //it returned the valued the value before adding 1, meanwhile x is 3
const r2 = x++ + 2 = 5
```

```
// decrement
let x = 5
const r3 = x-- = 5 //it returned the value before subtracting 1, x= 4
const r4 = x-- + 2 = 6
```

**PREFIX**

This returns the value of its operand **AFTER** adding 1 to it - **Increment**

This returns the value of its operand **AFTER** subtracting 1 from it - **Decrement**

```
let x = 5
const r5 = ++x = 6 //it returned the value after adding 1
const r6 = ++x + 2 = 9
```

```
let x = 5
const r7 = --x = 4 //it returned the value after subtracting 1
const r8 = --x + 2 = 5
```

Letβs mix both and see how it works

```
let x = 1
const a = x++ + x++= 3
const b = ++x + ++x = 9
const c = x++ + ++x = 12
const d = ++x + x++ = 16
```

try it out on your favorite code editor or you can view it on codepen

https://codepen.io/ojudith/pen/MWwZQxB