JavaScript - decrement operator

The decrement (--) is an unary operator in JavaScript and hence acts upon a single operand to produce a new value. It has two variant:

• Pre-decrement: Decreases the value of the operand by 1, then returns the operand.
• Post-decrement: Returns the operand, then decreases the value of the operand by 1.

Example: Pre-decrement operator

The example below describes the usage of pre-decrement operator.

var x = 10;
var y = 20;
var z, txt;

//below expression is equivalent to
//x = x - 1; z = x + y;
z = --x + y; 

txt = "x = " + x + "<br>";
txt = txt + "y = " + y + "<br>";
txt = txt + "z = " + z + "<br>";

The output (value of txt) after running above script will be:

x = 9
y = 20
z = 29

Example: Post-decrement operator

The example below describes the usage of post-decrement operator.

var x = 10;
var y = 20;
var z, txt;

//below expression is equivalent to
//z = x + y; x = x - 1; 
z = x-- + y;     

txt = "x = " + x + "<br>";
txt = txt + "y = " + y + "<br>";
txt = txt + "z = " + z + "<br>";

The output (value of txt) after running above script will be:

x = 9
y = 20
z = 30