Why modifying a JavaScript object prototype is not recommended

Discover the reasons why modifying a JavaScript object prototype can lead to problems and learn an alternative approach.

As software developers, one of the essential skills we learn early on is how to search for solutions to our coding challenges. Google becomes our best friend, and we often find answers on platforms like StackOverflow, even if they were posted many years ago.

While browsing through these resources, it’s not uncommon to come across code snippets that modify built-in object prototypes in JavaScript. For instance, consider the following example, where the Array object prototype is enhanced by adding an insert method:

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Array.prototype.insert = function(index, item) {
 this.splice(index, 0, item)
}

This modification allows you to call the insert() method on any array, as demonstrated here:

1	['red', 'blue'].insert(0, 'yellow')

This approach seems convenient because you avoid the need to define the insert function separately and worry about its scope. Instead, you attach it to the Array object, making it available to all arrays.

However, just because you can modify the prototype doesn’t mean you should.

Here are some reasons why this approach is not advisable:

Possible conflicts

Imagine you are using a library that also modifies the Array prototype, and that library implements a similar insert method. Problems can arise if both modifications work slightly differently or clash with each other. This situation becomes especially problematic when you don’t have control over those libraries but still need to use them.

Future-proofing your code

Consider the scenario where a future version of JavaScript introduces its own Array.insert method with a different signature. It means you would have to go back and rewrite all the code that relies on the modified prototype. This task can become particularly challenging if you are working on behalf of a client who no longer employs your services. Additionally, if others depend on your library, it becomes even worse.

By modifying object prototypes, you end up accumulating technical debt and invite potential problems in the long run.

So, what should you do instead?

Use a separate function

To avoid these issues, it is recommended to create a separate function in a library file. Whenever you need to use the functionality provided by that function, import it into your code. This way, you can achieve the desired behavior without modifying objects you don’t have control over.

By following this approach, you ensure a more maintainable and reliable codebase, reducing the chances of conflicting modifications and future compatibility issues.

Tags: JavaScript, object prototype, coding, future-proofing, maintainability