JavaScript - assignment operators example

The example below shows the usage of assignment and compound assignment operators:

= Assignment operator
+= Addition AND assignment operator
-= Subtraction AND assignment operator
*= Multiply AND assignment operator
/= Division AND assignment operator
**= Exponent AND assignment operator
%= Modulo AND assignment operator
&&= Logical AND assignment operator
||= Logical OR assignment operator
??= Nullish coalescing assignment operator

var X = 25;
var txt;

txt = "X = " + X + "<br>";

//Addition AND assignment operator
X += 5;
txt = txt + "X += 5; makes X = " + X + "<br>";

//Subtraction AND assignment operator
X -= 8;
txt = txt + "X -= 8; makes X = "+ X + "<br>";

//Multiply AND assignment operator
X *= 4;
txt = txt + "X *= 4; makes X = "+ X + "<br>";

//Division AND assignment operator
X /= 2;
txt = txt + "X /= 2; makes X = "+ X + "<br>";

//Exponent AND assignment operator
X **= 2;
txt = txt + "X **= 2; makes X = "+ X + "<br>";

//Modulo AND assignment operator
X %= 5;
txt = txt + "X %= 5; makes X = "+ X + "<br>";

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

X = 25
X += 5; makes X = 30
X -= 8; makes X = 22
X *= 4; makes X = 88
X /= 2; makes X = 44
X **= 2; makes X = 1936
X %= 5; makes X = 1

Logical AND assignment operator (&&=)

The logical AND assignment (x &&= y) operator only assigns if x is truthy (a value that is considered true in a Boolean context).

let a = 1;
let b = 0;
var txt;

//10 will be assigned to a
a &&= 10;
//no assignment is done to b
b &&= 10;

txt = "a = " + a + "<br>";
txt = txt + "b = " + b + "<br>";

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

a = 10
b = 0

Logical OR assignment operator (||=)

The logical OR assignment (x ||= y) operator only assigns if x is falsy (a value that is considered false in a Boolean context).

let a = 1;
let b = 0;
var txt;

//no assignment is done to a
a ||= 10;
//10 will be assigned to b
b ||= 10;

txt = "a = " + a + "<br>";
txt = txt + "b = " + b + "<br>";

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

a = 1
b = 10

Nullish coalescing assignment operator (??=)

The nullish coalescing assignment (x ??= y) operator only assigns if x is null or undefined.

let A = null;
let B = undefined;
let C = "Hello";

var txt;

//10 is assigned to a
A ??= 10;
//10 is assigned to b
B ??= 10;
//no assignment is done to c
C ??= 10;

txt = "A = " + A + "<br>";
txt = txt + "B = " + B + "<br>";
txt = txt + "C = " + C + "<br>";

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

A = 10
B = 10
C = Hello

❮ JavaScript - Operators