What is IIFE in JavaScript?

The first time I heard 'IIFE' in my Coding Bootcamp class, it immediately reminded me of my sister's dog 'Yeffi' which means 'pretty' in some human language.

So what is IIFE in JavaScript language?

IIFE stands for Immediately Invoked Function Expression. It is a JavaScript function that runs as soon as it is defined.

Normally, when we create a function using 'Function Declaration' or 'Function Expression', we need to call the function in order to use it.

Function Declaration:

function myFunction(p1, p2) {
    return p1 * p2;
}
alert(myFunction(4, 3));
//12

Function Expression:

let myFunction = function(p1, p2){
    return p1 * p2;
}
alert(myFunction(4,3));
//12

However, in IIFE, the function is wrapped in a parenthesis which makes it a function expression followed by () which tells the JavasScript compiler to invoke or call immediately.

(function() {
   let dName = "Yeffi";
   alert(dName);
}
)();
//Yeffi

So why do we use IIFE?

Mainly because of privacy. Any variables declared inside the IIFE are not accessible from the outside world.

(function() {
   let dName = "Yeffi";
}
)();

console.log(dName);
//  Uncaught ReferenceError: dName is not defined

If you try to access the dName variable outside of the IIFE, you get the error message as you can see above. All the variables inside the IIFE stay within the scope of the function.
Also, it protects the global namespace by not creating a named function. When a named function lingers in the global namespace, it could accidentally be called again. However, since IIFE isn't a named function, it can't accidentally be called. This will avoid any potential security implications. Therefore, many JavaScript libraries use this technique nowadays.

Thanks for reading!