IIFE(Immediately Invoked Function Expression)

IIFE = Immediately Invoked Function Expression 

 invokes itself when defined

normal JS function 

function () {

  // Code to run

};

Parentheses(fn) around the function tell JavaScript to treat the function as an expression.

(function () {

  // Code to run immediately

})

Function expressions will execute automatically if the expression is followed by ().

(function () {

  // Code to run immediately

})();

eg:

with arrow function () =>

(() => { 

  // Code runs immediately here 

})();

src:

https://www.w3schools.com/js/js_function_iife.asp

JavaScript modules often replace the need for IIFEs.

Modules have their own scope by default

IIFEs cannot be called again.