Script for reading relaxed json from stdin and returning formatted json

formatRelaxedJson.js

#!/usr/bin/env node

const vm = require('node:vm')
const readline = require('node:readline')

// Safely parse relaxed json from stdin and return formatted result.
// Intended for use from within VIM.
//
// Requirements:
//   1. Linux shell
//   2. NodeJS must be installed
//   3. Executable flag set on script file: chmod u+x formatRelaxedJson.js
//
// Command line:
// 
//   echo "{ foo: 'bar' }" | ./formatRelaxedJson.js
//
//
// VIM:
//   Press your leader key and then 'fj' to convert the whole file.
//   Also works in visual mode so you can select just the json to format
//
//   .vimrc:
//     " assumes formatRelaxedJson.js is located in your home directory...
//     nnoremap <Leader>fj :%! ~/formatRelaxedJson.js<CR>
//     vnoremap <Leader>fj :! ~/formatRelaxedJson.js<CR>
//
// Credit for use of node:vm goes to ojosilva:
// https://stackoverflow.com/a/76044884/219238

async function main () {
  const parts = []
  for await (const line of readline.createInterface({ input: process.stdin })) {
    parts.push(line)
  }
  const badJson = parts.join('\n')
  const parsedJson = parseRelaxedJson(badJson)
  console.log(JSON.stringify(parsedJson, null, 2))
}

function parseRelaxedJson (badJson) {
  try {
    const parsedJson = new vm.Script(`x=${badJson}`).runInNewContext(
      { console: undefined }, // nuke console inside the vm
      { timeout: 1000, displayErrors: true }
    )
    if (typeof parsedJson !== 'object') {
      // in case you're expecting an object/array
      throw new Error(`Invalid JSON=${badJson}, parsed as: ${parsedJson}`)
    }
    return parsedJson
  } catch (err) {
    throw new Error(`Could not parse JSON: ${err}`)
  }
}

main()

Motivation for this script was a tool that works on "relaxed" json rather than requiring the input json to be well-formatted like these do:

:%!jq .
:%!python -m json.tool

This script may also be helpful to those interested in:

• Creating a nodejs script that can be executed on the command line
• Reading in from stdin
• Using a VM to safely do parsing
• Configuring .vimrc to map both in normal and visual mode
• Sending buffer contents to a general shell script