Understanding IIFE Scoping in Javascript: Why is My Value Not Changing?

Explore the intricacies of `IIFE` (Immediately Invoked Function Expression) in Javascript. Learn how value scoping works, and discover solutions for cases where expected behavior doesn’t match reality.
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Understanding IIFE Scoping in Javascript: Why is My Value Not Changing?

Javascript is a powerful programming language that has its own quirks, especially around scoping and closures. One such feature is the Immediately Invoked Function Expression (IIFE). In this guide, we’ll explore a common problem developers face with IIFE scoping and how to understand and solve the issues it brings.

The Problem: Unexpected Value Behavior

Let’s start by looking at a specific challenge encountered while working with IIFE. Consider the following code snippet where we declare an IIFE and manipulate a value:

[[See Video to Reveal this Text or Code Snippet]]

What’s Going On?

After invoking iife.setValue("New"), you would expect iife.myValue to reflect the new value. However, running console.log(iife); right after reveals that myValue still holds the value "Previous". This discrepancy prompts questions about how IIFE scoping works.

The Solution: Understanding Closure and Scoping

Key Terms to Know

IIFE: A function that is executed immediately after its definition.

Closure: A feature where a function retains access to its lexical scope even when the function is executed outside that scope.

Scope: The context in which a variable exists and can be accessed.

Here's How It Works

Function Execution: When the IIFE runs, it creates its own scope. The variable myValue is not exposed outside this scope.

Returning Objects: When we return an object that includes myValue, we are creating a copy of the initial state of the variable at the time of the return.

Setters and Getters: The setValue function modifies myValue within the IIFE's scope. However, the myValue property of the returned object remains unchanged as it holds the initial value.

Changing the Code for Clarity

To visualize the behavior, you can add a setInterval function to log the value of myValue continuously:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion:

When you run this modified code, you will see that the log will reflect whatever new value you set using iife.setValue(). This demonstrates the power of closures — although myValue is not public, it is still modifiable within the IIFE’s scope, allowing accessor functions like getValue to provide the updated value.

Takeaway

The behavior observed with IIFE scoping might initially be confusing, especially when dealing with closures in Javascript. However, understanding how scoping works will pave the way for more effective coding. When working with IIFE, remember:

The encapsulated variables are private to the IIFE.

Use getter and setter functions to manipulate and access those values.

Always keep in mind that returned object properties represent copies of the initial state at the time of creation.

With this foundational understanding, you should feel more confident navigating the intricacies of Javascript and IIFE scoping!

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