ts-expect | Checks TypeScript types match expected values | Testing library

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I have a function that takes a second argument which is only required when the first argument is a string matching a template literal string. However, it appears that even when TypeScript knows that the first argument is such a string, it still matches the overload that takes a regular string:

I can't seem to figure out how to write a return type for this function, which works as expected, and typechecks as expected too (sans the internal todos). The fact that partially the type is on the inner closure is throwing me off.

Here's the core code, full code here:

The code is basically for a thumbnail-uploader accepting only SVGs. The problem is at new FileReader() and new Image().Can't understand the error Expected a spy but got a function upon it's execution. Function that I'm trying to test.The function is for a NgbModal that shows up for the preview purpose of uploading a thumbnail.The uploaded thumbnail first loads on the modal then at the component

So I have a union of tuples, and I can use it to declare locals:

Before this is marked as a duplicate, it is not, at least not of any of the first 10+ search results. This situation adds a level of complexity that I can't quite figure out.

tl;dr What works for exclusively specifying exactly one property of n must exist, or that a property must exist in exactly one of n spots, does not work when used on a nested property. TS Playground

I'm doing some Saturday overengineering--like ya do. My project uses JSON HAL documents (HAL documents basically describe an entity of some sort and with a _links property, define the available behavior), however, the backend (which I did not write) does not always send the documents in the same shape. I have a normalizeRepresentation() function that takes in what the server sends me and morphs it into what it should look like.

To produce minimal code, I've removed stuff regarding _links.

Differences between standard HAL:

• the entity data is on exactly one of:
  • the root document itself
  • the document property
  • the data property
  • the item property
  • the item.data property
• there is an optional contentType property that is either placed on the root document or inside the entity data, but not both

normalizeRepresentation() initially had the signature:

In a static method in a base class, is it possible to name the currently class's instance type?

Put another way, can you make this code type check:

I have a generic function to update state (use-case is dynamically handling updates to tables in React), and have used generics to ensure calling the function is type-safe, but I don't understand why TypeScript won't compile.

In the function itself it seems like Typescript isn't using all the available information to narrow down the type, and instead thinks I'm still working with the full union. It clearly knows enough about the arguments to tell whether the function is being called correctly, so why does it fail when type-checking the actual implementation?

Fails at row[field] = value.

Minimal example:

Is it possible to make //ts-expect-error directive only cover a concrete error and not others?

Example of code I would like to silent but only for some kind of error:

Error TS2588

Error TS2339

I would expect something like ESLint does with rules: //@ts-expect-error TS2339 to only silent errors of that kind, for example.

Using Typescript 4.1.2 is it possible to compile code that references the functions one calls when the --allow-natives-syntax flag in v8 is set?

For example: