Missing property types on the function object

[samuelhulla]

Information:

• VSCode Version: 1.47.3
• OS Version: Darwin x64 19.4.0

Steps to Reproduce:

1. Create a typescript project with enabled live typescript check in vscode.
2. Attempt to access typescript function properties

const example = (
   callback: (...args: unknown[]) => unknown
): void => {
 try {
    callback()
 } catch (e) {
    const raisedError = {
       name: callback.name // <- issue here
       // ....
    }
  }
}

The following line produces the following error:

name: callback.name // Property 'name' does not exist on type '(...args: unknown[]) => unknown'

Despite the fact these properties are accessible in the Function object.

Other information:

• Typescript in my project (package.json) is "ˆ3.9.7" (which is the latest version as of the day of this issue being posted)
• In my defaultSettings.json the typescript.tsdk is set to null (so it should use the latest version from package.json if I'm not mistaken)

• Does this issue occur when all extensions are disabled?: Yes

• This issue does not occur, if you try to reproduce it on

  • Codesandbox.io
  • typescriptlang.org/player
  • atom (with ts extensions)

• Link to StackOverflow thread

[samuelhulla]

For anyone else who encountered this issue, typecasting the value as any does solve the error, but it really is more of a workaround than solving the issue, so I would not recommend doing this unless you have to

name: (<any>callback).name // no longer throws error 

[mjbvz]

Works fine for me in VS Code insiders with TS 3.9.7 and with latest TS nightlies:

Do you have a tsconfig? If so, can you share it

[samuelhulla]

@mjbvz

// tsconfig.json
{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "declaration": true,
    "outDir": "./lib",
    "baseUrl": "./src",
    "strict": true
  },
  "include": ["src"],
  "exclude": ["node_modules", "**/__tests__/*"]
}

[mjbvz]

Still doesn't reproduce for me. Do you see this same error if you open a new folder in VS Code and create a single TS file with that content?

[samuelhulla]

@mjbvz Hmm strange, indeed. Seems to work fine in a new file. Here's the link to the file in question (although as you can see i slightly simplified the issue here, but it acts the same)

Also the entire repo is publicly available, so you can check the entire setup.
https://github.com/samuelhulla/react-eformless

[samuelhulla]

@mjbvz Actually I found out the issue which was causing it.

The reason for this error is that interface Functon has only been declared in lib.es6.d.ts

So depending on the needs, in order to solve this, you can

• Either upgrade the target version in tsconfig.json

  {
    "compilerOptions": {
       "target": "es6" // was "es5"
       // ...
    }
  }

• Or specify the "lib" to be included in compilation

  {
    "compilerOptions": {
        "lib": ["es6", "dom", "es2016", "es2017", "es5"], // needs at least es6
       // ...
    }
  }

[mjbvz]

Function.prototype.name was non-standard before ES6 (although widely supported). This error is likely by-design but I'll wait for a TS team member to confirm

[RyanCavanaugh]

Compare
https://www.ecma-international.org/ecma-262/5.1/#sec-15.3.5
to
http://www.ecma-international.org/ecma-262/6.0/#sec-function-instances

name is only present in the latter