Does it follow standard practice for Array.filter to have the capability to also perform mapping on an array of objects?

While experimenting with Array.filter, I made an interesting discovery. By forgetting to include an equality check, my array was unexpectedly mapped instead of filtered. Here is the code snippet that led to this result:

const x = [{ name: 'user' }];
console.log(x.filter(x => x.name = 'another user'))

// Result:
// [{ name: 'another user' }]

Has anyone else experienced this behavior before? I couldn't find any documentation on Array.filter behaving like Array.map as well. Could this be a feature or a bug? Perhaps I should report this on GitHub for further clarification...

Answer №1

There is a multitude of array methods that can iterate through every element of the array unless they are stopped prematurely in some way (like through an error being thrown, a callback returning a falsey value in Array.every, or a callback returning a truthy value in Array.find).

All of these methods can be misused to accomplish tasks they were not intended for. There are no exceptions, perhaps apart from the generic iteration methods specifically designed for side effects.

It is possible to misuse .filter as a replacement for a generic iteration method by including side effects within the callback. Similarly, .map can also be misused in the same manner.

If you wish to protect yourself from these types of mistakes, consider using a linter that can alert you about them, like ESLint's no-return-assign rule.

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