microsoft / microsoft/TypeScript
Inference for Object.isPrototypeOf()
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Description
Hi, I am wondering would be possible to infer types for isPrototypeOf() function same way as it's done with instanceof operator? So we could narrow type of argument if it's been created using Object.create(proto) function and its type would be something like typeof proto if check is fulfilled.
Search Terms
isPrototypeOf
Examples
if (object instanceof HTMLAnchorElement) {
console.log(object.href);
}
if (HTMLAnchorElement.prototype.isPrototypeOf(object)) {
console.log(object.href);
}
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
No implementation file, test, or entry point is identified in the issue. Start by locating the existing type narrowing for instanceof, then evaluate how the Object.isPrototypeOf() examples should narrow objects created with Object.create(proto); done means the proposed behavior is specified and covered by appropriate compiler tests.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript, typescript
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100