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Discover how to identify `new` properties added to JavaScript objects without inheriting from their base class. Learn simple techniques to simplify this process!
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How to List New Members of a JavaScript Object Not Inherited from Base Class

In the world of JavaScript, managing object properties effectively becomes crucial, especially when it involves understanding which properties are unique to an object versus those inherited from its prototype chain. If you've ever wondered how to list these unique or new members of an object, especially those that are not instance or static members from the base or inherited class, you've come to the right place!

The Challenge: What Are New Members?

When you add properties to an object in JavaScript, especially to something like the global window object, it can sometimes be challenging to differentiate between existing properties and new additions. This is particularly important in scenarios where scope and properties may change frequently, such as dynamic applications or while debugging.

Example Scenario

Consider the following code snippet:

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

The goal is to create a function, ListNewMemberNames, that will correctly identify and list properties that are newly added to the window object.

The Solution: Identifying New Members

While JavaScript doesn't provide a built-in way to dynamically analyze variable names or properties at the current scope, there is a method we can utilize. By taking a snapshot of the properties before and after making changes, we can effectively identify the new properties.

Step-by-Step Approach

Capture Existing Properties: Before adding new properties, store the current state of the window object’s properties using Object.getOwnPropertyNames().

Modify the Object: After capturing the properties, you can add your new properties (like var1).

Compare States: Finally, compare the new state of the window object with the initial state to see which properties have been newly added.

Here's how this can be implemented in code:

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

Explanation of Code

Object.getOwnPropertyNames(window): This method retrieves an array of all properties—both enumerable and non-enumerable—of the window object at the moment it is called.

filter Method: After adding var1, we retrieve the properties of window again and utilize the filter function to identify those properties which were not present in the initial snapshot.

Conclusion: Why Bother?

While identifying new members of an object can be useful for debugging or understanding state changes in your application, it should also be approached with caution. There may not always be a compelling reason to track these changes in practice because it can add complexity to your code. However, acknowledging this technique can deepen your understanding of JavaScript objects and their properties.

By following the steps and explanations provided above, you now have a robust method to identify newly added properties to objects in JavaScript—making your coding journey both informed and efficient!

Happy coding!