Typescript example doesn't compile

Hello,

I’m trying to use yargs with typescript but receive errors even after copying code from the docs.

The interesting part is that it starts to work after I await for result of argv.

Here is the text of error:

Element implicitly has an 'any' type because expression of type '"a"' can't be used to index type '{ [x: string]: unknown; a: boolean; b: string; c: number | undefined; d: (string | number)[] | undefined; e: number; f: string | undefined; _: (string | number)[]; $0: string; } | Promise<{ [x: string]: unknown; a: boolean; b: string; c: number | undefined; ... 4 more ...; $0: string; }>'.
  Property 'a' does not exist on type '{ [x: string]: unknown; a: boolean; b: string; c: number | undefined; d: (string | number)[] | undefined; e: number; f: string | undefined; _: (string | number)[]; $0: string; } | Promise<{ [x: string]: unknown; a: boolean; b: string; c: number | undefined; ... 4 more ...; $0: string; }>'

Here is my tsconfig:

{
  "compilerOptions": {
    "target": "esnext",
    "module": "commonjs",
    "strict": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "resolveJsonModule": true,
    "outDir": "dist",
    "lib": ["ESNext"]
  },
  "include": ["./src/**/*"]
}

I’m using:

"@types/yargs": "^17.0.0",
"yargs": "^17.0.1"

Thanks in advance

[kitesi]

As you can see from the error, the type of argv is a union. The first item is the arguments and the second one is a promise which resolves to those arguments. That is why when you await it, it gets the correct type.

The reason it’s a union is because in yargs you can have commands, and the handlers for those commands can be asynchronous. And so .argv would resolve after that command finishes.

In the example, you aren’t using any asynchronous commands, but yargs typing doesn’t know that when you are just calling .argv or .parse.

What you need to do is use #parseSync which explicitally tells yargs you have no asynchronous commands (this will also throw errors if there are async commands).

#!/usr/bin/env node
import yargs from 'yargs/yargs';

const argv = yargs(process.argv.slice(2)).options({
  a: { type: 'boolean', default: false },
  b: { type: 'string', demandOption: true },
  c: { type: 'number', alias: 'chill' },
  d: { type: 'array' },
  e: { type: 'count' },
  f: { choices: ['1', '2', '3'] }
}).parseSync();

argv.b // no error

[mafo5]

Thanks. Exactly what I am looking for. Should be in the documentation!