Instead of using the generic directly we can create a mapped type by using keyof. This is good if when you need to work with the size parameter by its own. But it fails to compile with Type '1' is not assignable to type 'T[Extract, type 'string' is not assignable to type 'never' keyof. I'm still confused about why this isn't a bug. Typescript Type 'string' is not assignable to type, Typescript: Type'string|undefined'isnotassignabletotype'string', Typescript: No index signature with a parameter of type 'string' was found on type '{ "A": string; }, Type 'string | boolean' is not assignable to type 'never'. Successfully merging a pull request may close this issue. @KeithHenry if you put the as any after the property access, TypeScript will check that k is a valid key. interface Callback Argument of type is not assignable to parameter of type 'never' Argument of type 'number' is not assignable to parameter of type 'SetStateAction<{ count1: number; count2: number; }>' (In other words, the subset of keyof T that includes only string-like values.) Additionally, thanks to the magic of ExtractRouteParams, params has an inferred type of {userId: string}, so the reference to params.userId is type safe. . // 'string' is a primitive, but 'String' // is a wrapper . It seems that most modern build tools (Vite, Parcel, etc) advertise TypeScript support but by that they mean these tools simply ignore types and then transpile assets.I'm torn. Other Answers: This has caused a very large number of errors for us with insufficient guidance of how to fix (from the release notes ). Argument of type '{ description: string; siteurl: string; }' is not assignable to parameter of type 0 Argument of type '10' is not assignable to parameter of type 'CanvasColumnFactor' any is not a set, and it undermines type-checking; so try to pretend that it does not exist when you can. Connect and share knowledge within a single location that is structured and easy to search. 1. this[stateItem as keyof ResetStateItems] = resetStateItems[stateItem]; 2. ecmascript-6 javascript typescript. OK, so we have large numbers of a pattern that looks like (from the OP): And these all fail because we have lots of boolean properties, and so TypeScript thinks the type of initState[k] is never (surely that's wrong?). And then it won't turn itself into a string anymore - which is the root of the problem in the question. For example, you have a function that accepts or returns a parameter of type size and you want to type it. seemed to me that it was the same as leaving the generics as default, since F and K are exactly the same as the default type. GitHub Pull Request #3504. Is there such a thing as "right to be heard" by the authorities? you are creating a type called Fruit that can only contain the literals "Orange", "Apple" and "Banana". Type 'string' is not assignable to type 'number'. the problem is that the expression result[key] has type never, which is a type with no values. Type 'string' is not assignable to type 'E'. I made a mistake in my original post. However, you might ask why node.name is implicitly cast to never (and [node.name] to ConcatArray) in the first place.I found an answer for this in this Github issue reply:. Here is the first example of how the error occurs. "logoff" : never'.ts(2345) It's easily circumventable using as: spyOn(this as AuthServiceMock, 'logoff'); But this shouldn't be necessary, so I thought I'd share my findings. User without create permission can create a custom object from Managed package using Custom Rest API, I like the way a string constant looks vs. an enum - it's compact and 'javascripty'. Facebook. . This question was tagged Angular even though it's not really anything to do with Angular. TypeScript Version: broken in: 3.3.3333 works in: 3.1.4 Search Terms: Mapped type key is wrong type. Keyof Type Operator - Using the keyof operator to create new types. Property 'toPromise' does not exist on type 'Observable'. But I don't follow why this is unsound. String is less specific. train station pub happy hour type 'string' is not assignable to type 'never' typescript. Argument of type '"vertical"' is not assignable to parameter of type 'Orientation'. argument of type any is not assignable to parameter of type never. Learn more Let's take as an example a simple interface representing a blog post. Just another site. interface Callback Patricia Sistine Skakel, Articles T