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JavaScript tip: How to properly isolate your code using Anonymous Closures (IIFEs)

December 30, 2019

JavaScript code can get really messy when we keep adding random functionalities as the requirements come.

And most of the times, any new functionality you add to an app should not interfere with the existing code in your app.

You don’t want the new piece of code to override your existing variables/functions accidentally. When such code causes some unexpected behaviour, it can get really annoying to debug through multiple files.

To achieve this, our new code should run in an isolated environment. In JavaScript, closures can help us do that. Closures are the primary mechanism used to enable data privacy in JavaScript.

This is how an anonymous closures looks like:

(function () {
// ... all vars and functions are in this scope only.
// still maintains access to all global variables

Just put your code inside of this function, and it will have its own scope while keeping the global scope pollution-free.

This is also known as a Self-Executing Anonymous Function or Immediately Invoked Function Expressions (IIFEs).

Variables declared inside the closure are not accessible outside it, but it still can access/create global variables. (The use of global variables should ideally be avoided though, they are known to be evil.)

All of the code that runs inside this function lives in a closure, which provides privacy and state throughout the lifetime of our application.

If we need to, we can expose variables/methods by returning them in the function.

var result = (function () {
var name = "Harry";
return name;
console.log(result); // "Harry"
console.log(name); // "error, 'name' not defined"

JavaScript Closures is the main idea behind the Module Pattern in JavaScript, you can explore the basics of module patter here:

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