Fix/fix all to remove TS-specific constructs in JS files

Description

function foo(x: string) {

}

Type annotations can only be used in TypeScript files.

Contributor guide

Tech stack

javascripttypescript

Domain

developer experiencetooling

Issue type

feature

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

1-2 days

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

TypeScript compiler internalsquick fix API

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

40

Research direction

Examine the existing quick fix infrastructure in the TypeScript compiler, particularly the files in src/services/quickFix.ts. Identify how similar diagnostics (e.g., unreachable code) are handled. Implement a new quick fix that removes type annotations from JavaScript files when the error 'Type annotations can only be used in TypeScript files' is reported. Ensure the fix handles various cases like variable declarations, function parameters, and return types. Write tests covering these scenarios.