Understanding JavaScript Mixins: Why Object.assign Evaluates Getters Early

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The Problem with Early Getter Evaluation

Imagine you have the following mixin defined:

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You might expect that the getter and setter will only be activated when actually called with the correct this context—the custom element itself. However, this is where the confusion begins. When you run your code, you encounter an error:

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

What Went Wrong?

Example of Early Evaluation

Consider this simpler example:

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

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

How Does This Work?

Benefits of the Solution

No Early Evaluation: Your getters will not be evaluated before they are actually called, thereby enabling dynamic behavior based on the context.

Effective Mixins: You can create robust mixins that behave as expected, effectively enhancing your class without introducing unexpected errors.

Conclusion

With this knowledge, you can confidently implement mixins in your custom elements and prevent early evaluations that could disrupt your code's functionality.