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Loosen strictness of Array.prototype.includes() and Set.prototype.has() #60559
Description
🔍 Search Terms
Example:
const values = ['foo', 'bar', 'baz'] as const;
type ValidValue = (typeof values)[number];
function isValueValid(value: string): value is ValidValue {
return values.includes(value);
// ^^ ts error: Argument of type 'string' is not assignable to parameter of type '"foo" | "bar" | "baz"'
}This error seems counter intuitive as the entire point of includes is to check if value in foo.includes(value) is one of foo.
A Set and mySet.has(...) has the same issue.
✅ Viability Checklist
- 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, new syntax sugar for JS, etc.)
- This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
- This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals
⭐ Suggestion
I'd expect typescript to not show an error here.
💻 Use Cases
Now having to deal with the removal suppressImplicitAnyIndexErrors: true in typescript 5.6
Activity
[-]Loosen strictness of `Array.prototype.includes()`[/-][+]Loosen strictness of `Array.prototype.includes()` and `Set.prototype.has()`[/+]MartinJohns commentedon Nov 22, 2024
Duplicate of #60073 and many many more. Your search terms seem excessive, no wonder you didn't find any of them. I suggest limiting your search terms to a few related word, often with the
in:titlemodifier.IMO a type assertion is an appropriate workaround if this is intentional code.
sod commentedon Nov 22, 2024
sorry. Thank you for your time.
I didn't see that improving this was already discussed and/or rejected.
sod commentedon Nov 22, 2024
reopen because it's not a duplicate of #60073.
This ticket is not about making
Array.prototype.includes()smarter. It's about not throwing ants-errorfor 100% valid and deterministic usecase.MartinJohns commentedon Nov 22, 2024
This is a duplicate of #60073, #26255 and many others, ending up with #14520.
Your issue is the accepted type for
includes(), same as the other.And I have no clue what "strict property access" (from your use case) is about, that's completely unrelated.
sod commentedon Nov 22, 2024
I aggree that this is a duplicate to #26255. A 6 year old, with 27 upvotes closed duplicate. But a duplicate non the less.
Then I guess i have to write:
I hope nobody follows the recommendation on https://www.typescriptlang.org/tsconfig/#suppressImplicitAnyIndexErrors to use
@ts-ignore, as that IMO is even worse.Yes,
strict property accessmade no sense. Removed that now from the description. This issue appeared when flicking"suppressImplicitAnyIndexErrors": truetofalse. A setting change that became mandatory withtypescript@5.6.Sadly I can't show it in the playground, because
"suppressImplicitAnyIndexErrors": trueisn't available anymore, even if you select an older version.Fell free to close this issue.
MartinJohns commentedon Nov 22, 2024
Again, you can just use a type assertion, IMO the cleanest approach:
values.includes(value as ValidValue)sod commentedon Nov 22, 2024
Indeed that works. Not sure why. I internalized that whenever I had to restort to typecasting, that my underlying types or generics are incorrect.
Thank you.