JavaScript Comma Operator

A comma operator (,) mainly evaluates its operands from left to right sequentially and returns the value of the rightmost operand. A comma operator is used as a separator for multiple expressions at a place that requires a single expression. When a comma operator is placed in an expression, it executes each expression and returns the rightmost expression.

Syntax:

Expression1, Expression2, Expression3, ....so on

In the above syntax, multiple expressions are separated using a comma operator. During execution, each expression will be executed from left to right and the rightmost expression will be returned.

Example: Below is an example of the Comma operator.

javascript

<script>
    function x() {
        console.log('one');
        return 'one';
    }
    function y() {
        console.log('two');
        return 'two';
    }
    function z() {
        console.log('three');
        return 'three';
    }

    // Three expressions are
    // given at one place
    var x = (x(), y(), z());

    console.log(x);
</script>

Output:

one
two
three
three

Example: This example shows the use of the comma operator in Javascript.

javascript

<script>
    function x() {
        console.log('Welcome');
        return 'Welcome';
    }
    function y() {
        console.log('to');
        return 'to';
    }
    function z() {
        console.log('Geeksforgeeks');
        return 'Geeksforgeeks';
    }

    // Three expressions are
    // given at one place
    var x = (x(), y(), z());

    console.log(x);
</script>

Output:

Welcome
to
Geeksforgeeks
Geeksforgeeks

In the output, first of all, the function x() is executed then y(), and lastly z(). Finally, the comma operator returns the rightmost expression.

Example: The most useful application of the comma operator is in loops. In loops, it is used to update multiple variables in the same expression.

javascript

<script>
    for (var a = 0, b =5; a <= 5; a++, b--) {
    console.log(a, b);
    }
</script>

Output:

0 5
1 4
2 3
3 2
4 1
5 0

We have a complete list of Javascript Operators, to check those please go through the Javascript Operators Complete Reference article. 

Supported Browsers:

• Google Chrome
• Internet Explorer
• Firefox
• Apple Safari
• Opera