Why Should You Avoid Extending Native JavaScript Objects?

Extending Native Objects: A Bad Practice in JavaScript

Native JavaScript objects, such as Object and Array, are essential building blocks for developing applications. Extending these objects by adding custom methods or properties can seem like a convenient way to enhance functionality. However, seasoned JavaScript experts strongly advise against this practice. Why?

Breaking Other Code

Extending native objects alters their default behavior. While this may be beneficial for your own code, it can have unintended consequences when interacting with code from other sources. JavaScript relies heavily on object methods and iterators, and modifying native objects can disruption these operations.

For instance, extending Object.prototype with a new property could affect loops and iterators, leading to unexpected behavior or errors. Consider the example of adding a "should" getter to Object:

Object.defineProperty(Object.prototype, 'should', {
  get: function(){
    return new Assertion(Object(this).valueOf());
  },
  configurable: true
});

While this extension appears harmless, it can overwrite the default behavior of existing loops and iterators, potentially introducing bugs into external code.

Performance Considerations

Extending native objects can also affect performance. JavaScript engines optimize for default object behavior, and any modifications may introduce additional overhead. While performance hits may not be noticeable for minor modifications, extensive extensions can impact execution speed.

Maintainability and Reusability

Customizing native objects diminishes their reusability and maintainability. If code relies on extended native objects, it becomes difficult to understand and modify when integrated with other projects that may have different definitions for the same objects.

Conclusion

While extending native objects can provide short-term benefits, the long-term consequences often outweigh the advantages. Breaking code, performance issues, and maintainability concerns make this practice highly inadvisable. Instead, it is recommended to create custom classes or use third-party libraries to extend functionality without compromising the stability of native objects.

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