JavaScript Assignment

Assignment operators


With assignment statements you can set and/or re-set the value that is stored in the storage location. What that really means is simply that a value is copied into the variable. 

The basic assignment operator is equal (=). That operator will assign the value of its right operand to its left operand. For example:  x = y,  will assign the value of y to x. The other assignment operators are usually shorthand for standard operations.


Name Shorthand operator Meaning
Assignment x = y x = y
Addition assignment> x += y x = x + y
Subtraction assignment x -= y x = x - y
Multiplication assignment x *= y x = x * y
Division assignment x /= y x = x / y
Remainder assignment x %= y x = x % y
Exponentiation assignment x **= y x = x ** y
Left shift assignment x <<= y x = x << y
Right shift assignment x >>= y x = x >> y
Unsigned right shift assignment x >>>= y x = x >>> y
Bitwise AND assignment x &= y x = x & y
Bitwise XOR assignment x ^= y x = x ^ y
Bitwise OR assignment x |= y x = x | y

Learn more about JavaScript Operators

Various examples

Let's take a look at some examples.


When using the addition assignment operator the value of the right operand is added and assigns the result to the variable.

JS JavaScript - Addition

<!DOCTYPE html>
<html lang="en" xmlns="">
<p>Check out the addition functionality.</p>
<button onclick="testAddition()">Click me to do the calculation</button>
    function testAddition() {
        // Declare and assign values to some variables.
        x = 'foo'
        y = 3
        z = true
        // Number + Number -> addition
        alert(y += 5)
        // Boolean + Number -> addition
        alert(z += 2)
        // Boolean + Boolean -> addition
        alert(z += false)
        // Number + String -> concatenation
        alert(y += 'foo')
        // String + Boolean -> concatenation
        alert(x += false)
        // String + String -> concatenation
        alert(x += 'bar')


When the subtraction assignment operator is used it will subtract the value of the right operand from a variable and the result is assigned to the variable.

JS JavaScript - Subtraction

<!DOCTYPE html>

<html lang="en" xmlns="">
    <p>Test out some substraction</p>
    <button onclick="testSubstraction()">Click me to do the calculation</button>
        function testSubstraction() {
            x = 9
            alert(x -= 4)  
            alert(x -= 'foo')


When using the multiplication assignment operator a variable is multiplied by the value of the right operand and the result is assigned to the variable.

JS JavaScript - Multiplication

<!DOCTYPE html>

<html lang="en" xmlns="">
    <p>Test out some multiplication</p>
    <button onclick="testMultiplication()">Click me to do the calculation</button>
        function testMultiplication() {
            // Declare and assign a value to a variable.
            x = 9;
            alert(x *= 3)
            alert(x *= 'foo') 


When using the division assignment operator the variable is divided by the value of the right operand and the result is assigned to the variable.

JS JavaScript - Division

<!DOCTYPE html>

<html lang="en" xmlns="">
    <p>Test out some division</p>
    <button onclick="testDivision()">Click me to do the calculation</button>
        function testDivision() {
            // Declare and assign a value to a variable.
            x = 7
            alert(x /= 2)     
            alert(x /= 'foo') 
            alert(x /= 0)     


When using the remainder assignment operator a remainder is assigned to a variable.

JS JavaScript - Remainder

<!DOCTYPE html>

<html lang="en" xmlns="">
    <p>Test out some remainder</p>
    <button onclick="testRemainder()">Click me to do the calculation</button>
        function testRemainder() {
            // Declare and assign a value to a variable.
            x = 7
            alert(x %= 3)     
            alert(x %= 'foo') 
            alert(x %= 0)

Learn more about JavaScript Variables Learn more about JavaScript Var Learn more about JavaScript Let

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JavaScript is one of the 3 core language technologies of the World Wide Web that all web developers must learn:

1.      HTML to define the content of web pages.

2.      CSS to specify the layout of web pages.

3.      JavaScript to program the behavior of web pages.

JavaScript is a scripting or programming language that allows you to implement complex things on web pages. Every time a web page does more than just sit there and display static information for you to look at, displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. − you can bet that JavaScript is probably involved.

The benefits of using JavaScript are:

1.      You can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.

2.      Immediate feedback to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.

3.      Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.

4.      Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.


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