microsoft / microsoft/TypeScript
Argument types of functions with multiple declarations should be smarter.
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Domain: check: Control Flow
Suggestion
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Description
Search Terms
Suggestion
Argument types of functions with multiple declarations should be smarter.
Use Cases
As showed in example,b should be a number when we are sure that a is "b".But it still think b as a number|string.
Examples
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. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
- This feature would agree with the rest of TypeScript's Design Goals.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the example from the linked TypeScript Playground and inspect how multiple declarations affect argument types during control-flow narrowing. Done means the implementation and accompanying checks make b reflect the selected declaration when a is narrowed, without changing the shown runtime behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- typescript
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100