Difference between function expression vs declaration in JavaScript

Last Updated : 22 Feb, 2023

Function Declaration: A Function Declaration( or a Function Statement) defines a function with the specified parameters without requiring a variable assignment. They exist on their own, i.e, they are standalone constructs and cannot be nested within a non-function block. A function is declared using the function keyword.

Syntax:

function gfg(parameter1, parameter2) {
 //A set of statements
 }

Function Expression: A Function Expression works just like a function declaration or a function statement, the only difference is that a function name is NOT started in a function expression, that is, anonymous functions are created in function expressions. The function expressions run as soon as they are defined.

Syntax:

var gfg = function(parameter1, parameter2) {
 //A set of statements
 }

Example 1: Using a Function Declaration

javascript

<!DOCTYPE html>
<html>

<head>
    <title>Function Declaration</title>
</head>

<body>
    <center>
        <h1 style="color:green">GeeksforGeeks</h1>
        <h3>Function Declaration</h3>
        <script>
            function gfg(a, b) {
                return a * b;
            }
            var result = gfg(5, 5);
            document.write(result);
        </script>
    </center>
</body>

</html>

Output:

Example 2: Using a Function Expression

javascript

<!DOCTYPE html>
<html>

<head>
    <title>Function Expression</title>
</head>

<body>
    <center>
        <h1 style="color:green">GeeksforGeeks</h1>
        <h3>Function Expression</h3>
        <script>
            var gfg = function(a, b) {
                return a * b;
            }
            document.write(gfg(5, 5));
        </script>
    </center>
</body>

</html>

Output:

Difference between function expression vs declaration in JavaScript

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