Use commander in typescript

Question

I try to use commander in typescript and I could like to give a proper type to my cli. So I start with this code: ``` import * as program from "commander"; const cli = program .version("1.0.0") .usage("[options]") .option("-d, --debug", "activate more debug messages. Can be set by env var DEBUG.", false) .parse(process.argv); console.log(cli.debug) ``` But I get this error: ``` example.ts(9,17): error TS2339: Property 'debug' does not exist on type 'Command'. ``` So I tried to add an interface, as documented here: ``` import * as program from "commander"; interface InterfaceCLI extends commander.Command { debug?: boolean; } const cli: InterfaceCLI = program .version("1.0.0") .usage("[options]") .option("-d, --debug", "activate more debug messages. Can be set by env var DEBUG.", false) .parse(process.argv); console.log(cli.debug) ``` and I get this error: ``` example.ts(3,32): error TS2503: Cannot find namespace 'commander'. ``` From what I understand, `cli` is actually a class of type…

Accepted Answer

With your first code snippet and the following dependencies, I do not get an error:

```
"dependencies": {
    "commander": "^2.11.0"
},
"devDependencies": {
  "@types/commander": "^2.9.1",
  "typescript": "^2.4.1"
}
```

Typescript interprets `cli.debug` as `any`. I guess the type declarations have been updated. So, if you are fine with `any`, the problem is solved.

If you really want to tell Typescript the type of `debug`, declaration merging would in principle be the way to go. It basically works like this:

```
class C {
    public foo: number;
}

interface C {
    bar: number;
}

const c = new C();
const fooBar = c.foo + c.bar;
```

However, there is a problem: `program.Command` is not a type but a variable. So, you cannot do this:

```
interface program.Command {
    debug: boolean;
}
```

And while you can do this:

```
function f1(): typeof program.Command {
    return program.Command;
}

type T = typeof program.Command;

function f2(): T {
    return program.Command;
}
```

You can neither do this:

```
interface typeof program.Command {
}
```

Nor this:

```
type T = typeof program.Command;

interface T {
}
```

I do not know whether this problem could be solved or not.

Use commander in typescript

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