Explain IIFE with an example

IIFE

An IIFE (Immediately Invoked Function Expression) is a JavaScript function that runs as soon as it is defined.

Question

What is IIFE in Javascript? Hot it works? Write an example.

Thought process Pseudocode

1. Write a function to log some message for example

function foo() {
  console.log('my log message');
}

2. For now it's not called. You can call it with name of function and parentheses. Call function and see log message in console

foo();
/**
my log message
**/

3. But also you can call it immediately as IIFE. You need to put your function definition into parentheses and add parentheses to call it. Give a try:

Solution

(function foo() {
  console.log('my log message');
})();
// or function can be anonymous
(function() {
    console.log('my log message');
})();

Caveat

You can't use IIFE without parentheses on initialization.

// NON WORKING EXAMPLE
(function () {
    console.log('my log');  
});

You should add parentheses on end of function initialization:

// WORKING EXAMPLE
(function () {
    console.log('my log');  
})();