Difference between function expression vs declaration in JavaScript
Last Updated :
22 Feb, 2023
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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
<!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>
<!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:
25
Example 2: Using a Function Expression
<!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>
<!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:
25
