Typescipt 'any' is a code smell

Typescript is a really powerful tool for making javascript more maintainable, easier to refactor and faster to write. one of Typescript's strengths is that any javascript code is also valid Typescript so the migration of a legacy js codebase is easy! While using any is about convenience, I consider it a code smell. Why?

No advantage over vanilla js

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When you use the any type, you are saying "please don't typecheck this" typescript will ignore any error you may make in using this type,

Harder to change in the future

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When you use any, you change the contract for your application and make it harder to refactor in the future. since there is no type safety, it's inherently harder to reason about and change.

It's the bare minimum

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Using any (except in the cases listed below) makes your code inherently harder to maintain and reason about. It's impolite to not at least provide a minimal typedef for your code.

When to use any

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There are a few cases where using any is acceptable:

1. When you are using a library that doesn't have types
2. When you are using a library that has types but they are wrong
3. When you are using a library that has types but they are incomplete
4. When you are working with a legacy codebase that has no types, and you don't yet know what the types are

What to do instead

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instead of using any I recommend fleshing your types out as much as possible. Even if you only know part of the type definition, it's better to have something than nothing.

1type MyType = {
2    someField: number,
3    otherFunc(): void
4    // ...maybe other stuff
5}

The benefits here are numerous, namely that:

1. This is MUCH easier to refactor, even if it is incomplete
2. I get basic intellisense now when I use this type
3. The compiler will now complain if we use it incorrectly
4. You don't look lazy, yay!