Understanding Why typeof undefined Occurs in a JavaScript Class Using Pixi.js

Dive into the intricacies of JavaScript classes with this detailed guide on why `typeof undefined` occurs and solutions to rectify it, particularly when used within Pixi.js.
---
This video is based on the question https://stackoverflow.com/q/77159638/ asked by the user 'Gaming Gecko' ( https://stackoverflow.com/u/7626654/ ) and on the answer https://stackoverflow.com/a/77159670/ provided by the user 'Đinh Carabus' ( https://stackoverflow.com/u/1967864/ ) 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: JavaScript typeof undefined in class

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

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding Why typeof undefined Occurs in a JavaScript Class Using Pixi.js

JavaScript is a powerful and versatile programming language commonly used for developing interactive web applications. However, even seasoned developers sometimes encounter issues that leave them pondering. One such issue is the unexpected typeof undefined when working with variables in a class. In this guide, we will explore a commonly faced problem in JavaScript classes, particularly in the context of the Pixi.js library, and delve into effective solutions.

The Problem Explained

Consider a scenario where you have created a JavaScript class called DialogueChoice:

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

Upon creating a new instance of this class and calling the test() method, you are surprised to see undefined instead of number. This could lead one to believe that the class is losing its members. What could be going wrong here?

Understanding the Context

The problem arises when methods of the class are invoked through an event system, such as in Pixi.js, rather than directly calling them from within your script. Here’s where the binding of the function context becomes crucial.

The Core Issue

JavaScript functions have a specific context called an execution context. When you call a method like test(), it’s attached to the instance of your class. However, when this method is passed around (e.g., as a callback), it loses its original context. Instead, it refers to the global object (typically window), leading to unexpected behavior like returning undefined.

How to Fix It

Solution 1: Binding the Method

One effective way to solve this issue is to bind the method to the object instance when passing it:

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

By using .bind(dc), you ensure that this within the test method still refers to the dc object when it is ultimately executed.

Solution 2: Arrow Functions

An alternative solution involves wrapping the method call in an arrow function:

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

Arrow functions maintain their own scope, avoiding the loss of context. When used this way, the test() method retains access to the dc instance, allowing for the correct value of this.integer to be logged.

Conclusion

In summary, encountering typeof undefined in a JavaScript class can often be traced back to issues with method context, especially when working with event-driven architectures like Pixi.js. By either binding the method or wrapping it in an arrow function, you can ensure that your class members remain accessible, leading to the behavior you expect.

Remember, understanding the context of your methods is critical when working in JavaScript, as it can save you from confusion and unexpected behavior in your applications.

If you've found this exploration into JavaScript class behavior insightful or have additional questions, feel free to drop a comment below!

Видео Understanding Why typeof undefined Occurs in a JavaScript Class Using Pixi.js канала vlogize