Reimplementation of default uncaught exception handler of nodejs

error.js

// reimplementation of default uncaught exception handler of nodejs v7.2 in js
//
// produces the same output as default handler of nodejs
// handles inline source maps with sinlge source (as V8 does)
// does not handle non-inline source maps or maps with multiple sources
//
// [email protected], public domain

"use strict";

let util = require('util')
let Module = require('module')
let fs = require('fs')
let path = require('path')

process.on('uncaughtException', (e) => {
  handle_error(e)
});

function parse_stack_line(text) {
  let s = text.trim().split(' ').pop()
  if (s.startsWith('(')) s = s.slice(1,-1)
  let [fn,ln,col] = s.split(':')
  return {fn,ln,col}
}

function handle_error(e) {

  function output_source_line(fn,ln,col) {
    if (fs.existsSync(fn)) {
      log('generated file found')
      let dcode = fs.readFileSync(fn, 'utf-8')
      let cmnt = dcode.split('\n')[0]

      let convert = require('convert-source-map')
      let sm_json = convert.fromComment(cmnt).toJSON()

      const sm = require('source-map')
      const smc = new sm.SourceMapConsumer(sm_json)

      fn = smc.sources[0]
      let pos = smc.originalPositionFor({
        line: ln|0, column: col|0
      })
      ln = pos.line
      col = pos.column
    }
    let dirname = path.dirname(fn)
    let cwd = process.cwd()
    if (dirname.indexOf(cwd)==0)
      dirname = '.' + dirname.substring(cwd.length)
    let name = path.basename(fn)
    // output file name and position, source line and "^" marker
    console.log(dirname+'/\x1b[01;39m'+name+'\x1b[00;39m:'+ln)
    console.log(fs.readFileSync(fn,'utf8').split('\n')[ln-1])
    console.log(' '.repeat(col) + '^\n')
  }

  let stack = e.stack
  if (typeof stack != typeof void 0) {
    let ss = stack.split('\n')
    ss = ss.filter( s=>s.trim().startsWith('at '))
    let frame = 0 // last frame
    let {fn,ln,col} = parse_stack_line(ss[frame])
    try {
      output_source_line(fn,ln,col)
    } catch(e) {
      console.error(e)
    }
    console.log(stack)
  } else {
    console.error(e)
  }
}