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TypeScript JSDoc generic member function

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  TypeScript JSDoc generic member function Julio Di Egidio <julio@diegidio.name> - 2023-10-25 20:03 +0200
    Re: TypeScript JSDoc generic member function John Harris <niam@jghnorth.org.uk.invalid> - 2023-10-26 11:28 +0100
    Re: TypeScript JSDoc generic member function Julio Di Egidio <julio@diegidio.name> - 2023-10-26 16:25 +0200

#41477 — TypeScript JSDoc generic member function

I cannot seem to find a way to tell TypeScript with JSDoc that a
member function of some object/interface takes a type parameter.

Here is a minimal example illustrating the problem:

```js
/**
  * @template {unknown} T
  * @callback IGet
  * @param {string} key
  * @returns {T | undefined}
  */

/**
  * @typedef IGetter
  * @type {object}
      * _@template {unknown} T  // how to write this?
  * @property {IGet<T>} get
  */
```

Error: Cannot find name 'T'.

That of course can be done in TypeScript, but how to do it with
JSDoc?  Is it at all possible?

Link to TypeScript playground:
<https://www.typescriptlang.org/play?strictNullChecks=true&noUncheckedIndexedAccess=true&allowUnusedLabels=true&noUnusedLocals=true&noUnusedParameters=true&removeComments=true&target=1&module=1&pretty=true&isolatedModules=true&useUnknownInCatchVariables=true&exactOptionalPropertyTypes=true&noFallthroughCasesInSwitch=true&noImplicitOverride=true&noPropertyAccessFromIndexSignature=true&keyofStringsOnly=true&filetype=js#code/PQKhCgAIUgBAXApgWwA4BsCGTIG8CuAdgNaED2A7oQL6QAqUMsAxpuugEabPGQCSAcUTxGcVJgBOmZHgDO8CQEtCAc1rFEAT1GwJw-BMKy8dSAB9IRACaIAZssRXqjYOHCgI0OPE2pHd-iF4JAkdHz88Mg4AK0RmeGdIJKSYAH0EFAxsRDwiUkoaeiTgYEgAC0pIeDJICiUceDLFWQB+HVQJMj8JHzxBYQAeOgA+WhVhF3AgA>

Julio

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#41478

On 25/10/2023 19:03, Julio Di Egidio wrote:
> I cannot seem to find a way to tell TypeScript with JSDoc that a
> member function of some object/interface takes a type parameter.
> 
> Here is a minimal example illustrating the problem:
> 
> ```js
> /**
>   * @template {unknown} T
>   * @callback IGet
>   * @param {string} key
>   * @returns {T | undefined}
>   */
> 
> /**
>   * @typedef IGetter
>   * @type {object}
>       * _@template {unknown} T  // how to write this?
>   * @property {IGet<T>} get
>   */
> ```
> 
> Error: Cannot find name 'T'.
> 
> That of course can be done in TypeScript, but how to do it with
> JSDoc?  Is it at all possible?
> 
> Link to TypeScript playground:
> <https://www.typescriptlang.org/play?strictNullChecks=true&noUncheckedIndexedAccess=true&allowUnusedLabels=true&noUnusedLocals=true&noUnusedParameters=true&removeComments=true&target=1&module=1&pretty=true&isolatedModules=true&useUnknownInCatchVariables=true&exactOptionalPropertyTypes=true&noFallthroughCasesInSwitch=true&noImplicitOverride=true&noPropertyAccessFromIndexSignature=true&keyofStringsOnly=true&filetype=js#code/PQKhCgAIUgBAXApgWwA4BsCGTIG8CuAdgNaED2A7oQL6QAqUMsAxpuugEabPGQCSAcUTxGcVJgBOmZHgDO8CQEtCAc1rFEAT1GwJw-BMKy8dSAB9IRACaIAZssRXqjYOHCgI0OPE2pHd-iF4JAkdHz88Mg4AK0RmeGdIJKSYAH0EFAxsRDwiUkoaeiTgYEgAC0pIeDJICiUceDLFWQB+HVQJMj8JHzxBYQAeOgA+WhVhF3AgA>
> 
> Julio

That's the trouble with documentation programs. Users have no control 
over the program's prejudices.

   John

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#41479

On 25/10/2023 20:03, Julio Di Egidio wrote:
> I cannot seem to find a way to tell TypeScript with JSDoc that a
> member function of some object/interface takes a type parameter.
> 
> Here is a minimal example illustrating the problem:
> 
> ```js
> /**
>   * @template {unknown} T
>   * @callback IGet
>   * @param {string} key
>   * @returns {T | undefined}
>   */
> 
> /**
>   * @typedef IGetter
>   * @type {object}
>       * _@template {unknown} T  // how to write this?
>   * @property {IGet<T>} get
>   */
> ```
> 
> Error: Cannot find name 'T'.
> 
> That of course can be done in TypeScript, but how to do it with
> [TypeScript's] JSDoc?  Is it at all possible?

I was wrong, that cannot be done in TypeScript either...

Eventually, the only way I have found is to repeat the
declaration in-line, as in:

```js
/**
  * @typedef IGetter
  * @type {object}
  * @property {<T extends unknown>(key: string) => (T | undefined)} get
  */
```

but I lose any chance to properly document that function, which
is simply quite a disaster: and not the only one, also the return
type gets messed up (becomes just `T`), to the point that I am
compelled to do something altogether different, i.e. have a
concrete object constructor.

File under the misery of an entire industry.

Julio

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