Difference between function expression vs declaration in JavaScript

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

filter_none

edit
close

play_arrow

link
brightness_4
code

<!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>

chevron_right


Output:

25

Example 2: Using a Function Expression

filter_none

edit
close

play_arrow

link
brightness_4
code

<!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>

chevron_right


Output:

25


My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.