build fails in "npm i" - tsc errors: 'err' is of type 'unknown'.

[DavidBiesack]

I cloned this repo and tried to build locally (to try to debug/fix an issue I reported).

The npm i command failed in tsc

$ npm i

> ajv-cli@5.0.0 prepublish
> npm run build


> ajv-cli@5.0.0 build
> rimraf dist && tsc

src/commands/ajv.ts:89:11 - error TS18046: 'err' is of type 'unknown'.

89       if (err.code === "MODULE_NOT_FOUND") {
             ~~~

src/commands/ajv.ts:91:110 - error TS18046: 'err' is of type 'unknown'.

91           `'ts-node' is required for the TypeScript configuration files. Make sure it is installed\nError: ${err.message}`
                                                                                                                ~~~

src/commands/util.ts:55:25 - error TS18046: 'err' is of type 'unknown'.

55     const msg: string = err.message
                           ~~~

src/commands/util.ts:85:29 - error TS18046: 'err' is of type 'unknown'.

85     console.error(`error: ${err.message}`)
                               ~~~


Found 4 errors in 2 files.

Errors  Files
     2  src/commands/ajv.ts:89
     2  src/commands/util.ts:55
npm ERR! code 2
npm ERR! path ~/dev/tools/ajv-cli
npm ERR! command failed
npm ERR! command sh -c npm run build

Opening the project in VSCode, I also see (other) errors such as

Cannot find module 'json5'. Did you mean to set the 'moduleResolution' option to 'nodenext', or to add aliases to the 'paths' option? ts(2792)

What version of Node.js is required to build? I tried Node 18 and 20

Please add a CONTRIBUTING file or build instructions to the README since this project does not build "out of the box".

(i.e. should I increment the package.json version when submitting a PR, or do maintainers do that when making a release, etc.)

[DavidBiesack]

I can wrap some of those err.message references with

  if (err instanceof Error) { ... }

but that does not address the reference to err.code === "MODULE_NOT_FOUND" in util.js .
Apparently, .code is defined in SystemError which Node does not export (see nodejs/node#46869 ); that takes more code to get past tsc compile warnings.
The following works, but it's not as elegant as an instanceof SystemError check:

    try {
      registerer = require("ts-node").register()
    } catch (err) {
      if (err instanceof Error) {
        if ((err as NodeJS.ErrnoException).code === "MODULE_NOT_FOUND") {
          throw new Error(
            `'ts-node' is required for the TypeScript configuration files. Make sure it is installed\nError: ${err.message}`
          )
        }
      }
      throw err
    }

With those code changes, the package compiles with tsc (via npm run build).

[DavidBiesack]

PR #242 addresses this in a different way (use (err: any) ).
I'll let maintainers decide whether this repo allows additional use of any type (there are some other places where any is used)