Strict type-checking on a per-file basis "@ts-strict"

Search Terms

strict per file

Suggestion

Currently in the process of converting a moderate-sized javascript project to typescript. Would love to be able to enable strict type-checks on a per-file basis.

Use Cases

Enabling strict mode for the entire project is a daunting task that presents a barrier to adoption (and using typescript without strict mode turned on is like locking the doors on a convertible....it's probably better than nothing, but it's not gonna keep you safe).

Examples

//@ts-strict

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

No files, tests, or entry points are named. Start by tracing how TypeScript reads per-file directives and applies strict compiler options, then determine how the proposed @ts-strict marker should interact with project-wide settings. Done means a per-file marker enables strict type-checking without changing emitted JavaScript or existing non-strict behavior.