HOWTO · JavaScript

How to Addition Assignment or += Operator in JavaScript

This article will let you know about the addition assignment operator in JavaScript. Let's have look how it works and read the other assignment operators.

By Muhammad Muzammil HussainPublished 2022-02-17Updated 2024-02-02

This article will inform you about JavaScript’s addition assignment operator. Let’s look at how it works and read the other assignment operators.

What Is += in JavaScript

The += is the addition assignment operator in JavaScript. It adds two values together and assigns the result to a variable in a single JavaScript statement.

Syntax:

x += y;
means x = x + y;
a += b;
means a = a + b;

The behavior of the addition assignment operator, either addition or concatenation, depends on the types of two operands, as explained in the following example.

<html>
    <head>
        <title>
            JavaScript addition assignment operator
        </title>
    </head>
    <body>
        <h3> <u> JavaScript addition assignment operator </u></h3>
    <body>
        <script>
            var a = 3;
            var b = "Delft"
            document.write(a += 5); // Addition
            document.write("<br>");
            document.write("<br>");
            document.write(b += "Stack"); // Concatenation
        </script>
</html>

Output:

JavaScript addition assignment operator
8
DelftStack

Example of JavaScript addition assignment operator:

<html>
    <head>
        <title>
            JavaScript addition assignment operator
        </title>
    </head>
    <body>
        <h3> <u> JavaScript addition assignment operator in different scenarios </u></h3>
    <body>
    <script>
        var  ds = 'DelftStack';
        var n = 4;
        var  b = true;

        // adding number with number results in addition
        document.write(n += 5);  // 9
        document.write("<br>");

        // adding Boolean with Number results in addition
        document.write(b += 1); // 2
        document.write("<br>");

        // adding Boolean with Boolean results in addition
        document.write(b += false); // 2
        document.write("<br>");

        // adding Number with String results in concatenation
        document.write(n += 'Cybexo') // "9Cybexo"
        document.write("<br>");

        // adding String with Boolean results in concatenation
        document.write(ds += false) // "DelftStackfalse"
        document.write("<br>");

        // adding String with String results in concatenation
        document.write(ds += ' Technology') // "DelftStack Technology"
    </script>
</html>

Output:

JavaScript addition assignment operator in different scenarios
9
2
2
9Cybexo
DelftStackfalse
DelftStackfalse Technology

Similarly, in JavaScript, we also have:

  • Subtraction assignment operator -=
  • Multiplication assignment operator *=
  • Division assignment operator /=
  • Modulus assignment operator %=

Use the -= as a Subtraction Assignment Operator

The subtraction assignment operator is used to subtract the right operand number value from a variable value and then assign the result to the variable.

Syntax:

x -= y;
means x = x - y;
a -= b;
means a = a - b;

Use the *= as a Multiplication Assignment Operator

The multiplication assignment operator multiplies a variable by the value of the right operand and then assigns the result to the variable in a single statement.

Syntax:

x *= y;
means x = x * y;
a *= b;
means a = a * b;

Use the /= as a Division Assignment Operator

It divides the variable by the right operand number and assigns the result to the variable in a single JavaScript statement.

Syntax:

x /= y;
means x = x / y;
a /= b;
means a = a / b;

Use the %= as a Remainder/Modulus Assignment Operator

The remainder/modulus assignment operator divides a variable by the value of the right operand and then assigns the remainder to the variable in a single JavaScript statement.

Syntax:

x %= y means x = x % y
a %= b means a = a % b

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Muhammad Muzammil Hussain

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