Prevent printing js errors attached fields

If you log a NodeJs error in the console it will also show all the fields attached, this is a problem for very long fields as they will make a mess in your terminal of CI.

For example having this custom error class:

typescript
export class ShellError extends Error {
    stdout: string
    stderr: string
    output: string
    constructor(message: string, stdout: string, stderr: string) {
        super(message)
        this.stdout = stdout
        this.stderr = stderr
        this.output = stdout + '\n' + stderr
    }
}
console.log(new ShellError('error', 'stdout', 'stderr'))

The console will show

shell
ShellError: error
    at Object.<anonymous> (/Users/morse/Documents/GitHub/docs-from-notion/local-scripts/play.ts:17:13)
    at Module._compile (node:internal/modules/cjs/loader:1103:14)
    at Object.m (/Users/morse/.volta/tools/image/packages/esno/lib/node_modules/esno/node_modules/@esbuild-kit/cjs-loader/dist/index.js:1:536)
    at Module.load (node:internal/modules/cjs/loader:981:32)
    at Function.Module._load (node:internal/modules/cjs/loader:822:12)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/translators:168:29)
    at ModuleJob.run (node:internal/modules/esm/module_job:197:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:337:24)
    at async loadESM (node:internal/process/esm_loader:88:5) {
  stdout: 'stdout',
  stderr: 'stderr',
  output: 'stdout\nstderr'
}

As you can see it shows the fields stdout and stderr. This is a big problem if these fields are very big because it will hide everything else in the console.

Fortunately there is a solution, you can use js private fields to hide the fields from NodeJs and add getters to allow retrieving them by your code:

typescript
export class ShellError extends Error {
    #stdout: string
    #stderr: string
    #output: string
    constructor(message: string, stdout: string, stderr: string) {
        super(message)
        this.name = 'ShellError'
        this.#stdout = stdout
        this.#stderr = stderr
        this.#output = stdout + '\n' + stderr
    }
    get output() {
        return this.#output
    }
}

Private fields are fairly new in javascript so you will need to transpile them away or use latest NodeJs.

❗

fields that start with # are called private fields and are not accessible outside of the class, that’s why we created the get output getter