Ability to disable TS8010: 'types' can only be used in a .ts file.

Search Terms

TS8010 TS 8010 types can only be used in a .ts file ‘types’ can only be used in a .ts file

Suggestion

Ability to disable TS8010: ‘types’ can only be used in a .ts file. Type annotations could simply be ignore by tsc when compiling a .js file.

Use Cases

I work in a JS / TS blended codebase. My team uses WebStorm as our IDE, and it supports type annotations in .js files. When a variable/param is typed, it provides type-specific autocompletion. As you can imagine, that’s quite powerful when working in a JS environment. Consequently, we have thousands of type annotations throughout our JS files. We would like to add allowJs:true to our tsconfig.json, however tsc throws an error for every type annotation in each JS file.

Checklist

My suggestion meets these guidelines:

• [ x ] This wouldn’t be a breaking change in existing TypeScript/JavaScript code
• [ x ] This wouldn’t change the runtime behavior of existing JavaScript code
• [ x ] This could be implemented without emitting different JS based on the types of the expressions
• [ x ] This isn’t a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• [ x ] This feature would agree with the rest of TypeScript’s Design Goals.

[alexkrolick]

I am in a similar boat with Flow => TS migration. The ideal configuration during the migration is checkJs: false, allowJs: true, so that we can import JS files (with Flow types) into the TS files. But tsc give me thousands of errors for Type annotations can only be used in TypeScript files when it tries to see if the JS files contain TS code and mistakes the Flow annotations for TS. We can compile the code using Webpack, but can’t do a static check in CI, with this setup.

[ValentinH]

This could also be a valid use case for me. Indeed, I’m migrating an app from Flow to Typescript.

Right now, I’m using allowJs: true in my config and it enables me to import JS modules written in Flow into a TS modle with a working type-check in VSCode. However, if I run tsc --noEmit to ensure that my ts files are valid, I get tons of TS8010 errors.

Being able to disable this during the migration would really help us.