Understanding the Array.map Method in JavaScript: How to Prevent Object Mutation

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The Challenge: Mutating the Original Array

Consider the following code snippet:

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In this example, the intention is to enhance each object in the obj1 array by adding a new property without altering the original obj1. However, the developer finds that obj1 is still being changed. Why does this happen?

Understanding Object References

In JavaScript, objects are stored as references. When the line let obj = e; is executed, you're not creating a new object. Instead, you're creating a reference to the same existing object in the array. Hence, when you modify obj, you're also simultaneously modifying the object in obj1. This is the root cause of the unintended mutation.

The Solution: Proper Object Copying

To prevent this issue, you need to create a new copy of each object before making any modifications. Below are two effective ways to achieve this:

1. Using the Spread Operator

The spread operator (...) is a concise way to create a shallow copy of an object. Here's how you can implement it:

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

Applying the Solution

By updating the myFunc function to use either copying technique, your final implementation would look like this:

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

Conclusion

By mastering these concepts, you will write cleaner, safer, and more predictable code. Happy coding!