microsoft / microsoft/TypeScript
Add type predicate to Object.is
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Domain: lib.d.ts
In Discussion
Suggestion
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Description
Search Terms
object.is
type predicate
Suggestion
When a is b, a and b has to same type, so I suggest adding a few generic overloads with type predicates
interface ObjectConstructor {
is<A, B extends A> (a: A, b: B): a is B
is<A extends B, B> (a: A, b: B): b is A
is (a: any, b: any): boolean
}
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
The issue proposes generic type-predicate overloads for Object.is but names no source files or tests. Start by locating the existing Object.is declaration and related type-predicate tests, then determine whether the proposed overloads are sound and what test coverage would demonstrate the intended narrowing 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