JavaScript IIFE stands for an immediately invoked function expression. It defined as a function expression and executed immediately after creation.
It is a design pattern which is also known as a Self-Executing Anonymous Function
Syntax
Defining an immediately invoked function expression:
(function(){
    //...
})();Immediately invoked function expression (IIFE) Example
Let’s see the HTML example of the function becomes a function expression that is immediately executed.
<!DOCTYPE html>
<html>
<head>
    <script>
        // Regular Function. 
        function msg() 
        { 
            console.log("Welcome to EyeHunts!"); 
        }; 
        // Execution of Regular Function. 
        msg(); 
        // IIFE creation and execution. 
        (function() { console.log("Welcome!"); })(); 
    </script>
</head>
<body>
</body>
</html>Output:

Note: The variable within the function expression can not be accessed from outside it.
Do comment if you have any doubts and suggestion on this topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version