Re:TypeScript 3.5
by WorldMaker on Wednesday May 29, 2019 @04:33PM
(#20045095)
> 'x' as 'x'
As others point out, 3.4 added `as const` which is more powerful and more generic.
> Add to that, in many cases being unable to import a JS library in that doesn't include typedefs, and I fail to see how TS can be considered a superset of JS. It's certainly sold that way, but it's clearly not totally true. TS+React requires --noImplicitAny, which cannot be worked around (it's labeled as being required due to a platform limitation).
No implicit any just restricts the type system from falling back to `any`, it doesn't stop you from explicitly using `any`. Most places where you get a noImplicitAny error you can add an `as any` or a `: any` assertion nearby. Explicit `any` is still often useful, even if only as a TODO marker for that day you can search for `any` in the codebase and try to remove it.
There's also `as unknown` or `: unknown` type assertions as another option for `any` in some case (`unknown` is stricter than `any` and implies you are going to be testing the value for runtime type information).
Use an explicit `any` applies to modules too. That problem with importing a JS library but getting a noImplicitAny error can be solved with an explicit `any`. That's where one particularly useful real world case of `declare` comes in. Add a file called something like `modules.d.ts` (the `.d.ts` is a convention that it won't have actual TS code, just declarations) and then to add explicit `any` for any module you want to import is as simple as:
declare module "modulename";
`declare` is how you write type definitions for JS code. The simplest declaration is that a module exists and could be anything.
> I also find Microsoft's documentation of TypeScript to be very poor
There's a better documentation site being built with better search and with a lot more interactive examples. I don't know when it might be expected to be released, but BUILD talks seemed to indicate that Microsoft is aware that Typescript's documentation hasn't kept up with its release cadence and needs love.
As others point out, 3.4 added `as const` which is more powerful and more generic.
> Add to that, in many cases being unable to import a JS library in that doesn't include typedefs, and I fail to see how TS can be considered a superset of JS. It's certainly sold that way, but it's clearly not totally true. TS+React requires --noImplicitAny, which cannot be worked around (it's labeled as being required due to a platform limitation).
No implicit any just restricts the type system from falling back to `any`, it doesn't stop you from explicitly using `any`. Most places where you get a noImplicitAny error you can add an `as any` or a `: any` assertion nearby. Explicit `any` is still often useful, even if only as a TODO marker for that day you can search for `any` in the codebase and try to remove it.
There's also `as unknown` or `: unknown` type assertions as another option for `any` in some case (`unknown` is stricter than `any` and implies you are going to be testing the value for runtime type information).
Use an explicit `any` applies to modules too. That problem with importing a JS library but getting a noImplicitAny error can be solved with an explicit `any`. That's where one particularly useful real world case of `declare` comes in. Add a file called something like `modules.d.ts` (the `.d.ts` is a convention that it won't have actual TS code, just declarations) and then to add explicit `any` for any module you want to import is as simple as:
`declare` is how you write type definitions for JS code. The simplest declaration is that a module exists and could be anything.> I also find Microsoft's documentation of TypeScript to be very poor
There's a better documentation site being built with better search and with a lot more interactive examples. I don't know when it might be expected to be released, but BUILD talks seemed to indicate that Microsoft is aware that Typescript's documentation hasn't kept up with its release cadence and needs love.