Understanding Scope and Closure in JavaScript with Recursion and Helper Functions

Dive into the world of JavaScript by exploring the important concepts of `scope` and `closure` through recursion and helper functions. Learn how to properly manipulate variables across different scopes to write effective functions!
---
This video is based on the question https://stackoverflow.com/q/63964832/ asked by the user 'Kushh' ( https://stackoverflow.com/u/13847908/ ) and on the answer https://stackoverflow.com/a/63965398/ provided by the user 'Wilbur Hsu' ( https://stackoverflow.com/u/14213124/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to understand scope/closure with recursion and helper function?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding Scope and Closure in JavaScript with Recursion and Helper Functions

Programming often provides us with puzzles to solve and challenges to conquer. Today, we delve into a common JavaScript conundrum: how to understand scope and closure when using recursion and helper functions. Let's break down this concept through practical examples and explanations.

The Problem: Misunderstandings in Variable Scope

In JavaScript, it's crucial to grasp how scope and closure work, especially in more complex programming patterns like recursion. Let's explore two examples that illustrate the importance of correctly passing and manipulating variables within these contexts.

Example 1: Finding the Maximum Depth of a Binary Tree

When attempting to find the maximum depth of a binary tree, a common mistake arises in handling variable scopes. Here are two implementations of a function designed for this purpose:

Right Answer:

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

Wrong Answer:

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

What's the Difference?

In the right answer, the updated maxDepth is returned from the helper function, allowing for the correct maximum depth to be calculated and returned.

In the wrong answer, the helper function modifies the inner maxDepth, which does not affect the outer maxDepth variable.

The Insight: Understanding Variable Scope

The pivotal point to grasp here is how JavaScript handles variable assignments:

Primitive Values: When you assign a primitive value to a variable (like numbers or strings), it creates a new copy of that value. Changes to this copy do not affect the original.

Objects/Arrays: When you assign an object or an array to a variable, what you actually store is a reference (pointer) to that object or array. Therefore, if you modify what's pointed to by that reference, both variables will reflect the changes.

Memory Reference

In the first example, when you pass maxDepth to maxDepthHelper, you are effectively passing a value (1) that is copied to the local variable maxDepth within the function's scope. Thus, changes made inside the function do not reflect back on the outer variable.

Example 2: Finding the Kth Smallest Element in a Binary Search Tree

Let's look at a different scenario involving a binary search tree:

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

How Variables Interact Here

In this case, the smallestArr variable stores a pointer to an array. When you pass smallestArr to the helper function:

Both smallestArr and the array in kthSmallestHelper point to the same array.

If you push elements into array, smallestArr reflects those changes since they point to the same memory location.

Conclusion: Mastering JavaScript Scopes

Understanding scope and closure in JavaScript is essential, especially when dealing with recursion and helper functions. Remember:

Variables that are primitive types can be passed by value and do not affect the outer variable.

Variables that are objects or arrays can be passed by reference, implying shared pointers, where changes affect the original variable.

Mastering these concepts will significantly enhance your ability to write effective JavaScript functions. Happy coding!