Skip to content

replace implicit 'any' with 'unknown' #27265

Open
@mmkal

Description

@mmkal

Search Terms

noImplicitAny, strict, any, unknown

Suggestion

When enabling "strict": true or "noImplicitAny": true in a project, could we assign unknown to un-inferred/un-typed variables, instead of causing a compiler error? This would be a non-breaking change, since all cases where this would have an effect are already compiler errors.

Use Cases

It would allow avoiding having to specify a type when it's being type-checked anyway. The current implementation forces converted-from-js projects to deal with a lot of compiler errors from the outset (many of which use various runtime type-checking methods so should be happy with implicit unknowns).

Examples

const getMessage = input => typeof input === 'string' ? input : 'hello';
const shortenMessage = message => message.substring(3);

the getMessage example would be an error currently, but would be fine in the new world and the function would have return type string.
the shortenMessage example would have a changed error. instead of Parameter 'message' implicitly has an 'any' type we'd see an error at message.substring of Object is of type 'unknown'. To me that's more intuitive in terms of what the problem actually is. message is unknown so it should have type unknown.

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)

Metadata

Metadata

Assignees

No one assigned

    Labels

    Add a FlagAny problem can be solved by flags, except for the problem of having too many flagsAwaiting More FeedbackThis means we'd like to hear from more people who would be helped by this featureSuggestionAn idea for TypeScript

    Type

    No type

    Projects

    No projects

    Milestone

    No milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions