cost-of-modules Unexpected end of JSON input

First of all I love this utility, thanks for making!

I am getting the following error:

SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at getDependencyTree (/Users/me/.config/yarn/global/node_modules/cost-of-modules/lib/helpers.js:64:17)
    at Object.getRootDependencies (/Users/me/.config/yarn/global/node_modules/cost-of-modules/lib/helpers.js:73:26)
    at Object.<anonymous> (/Users/me/.config/yarn/global/node_modules/cost-of-modules/lib/index.js:26:32)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)
    at tryModuleLoad (module.js:466:12)
    at Function.Module._load (module.js:458:3)
    at Function.Module.runMain (module.js:605:10)

My package.json is:

{
  "name": "gtest",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "devDependencies": {
    "gulp": "gulpjs/gulp#4.0",
    "gulp-cli": "^1.3.0"
  }
}

I am using npm 5.0.0, and I suspect that the issue relates to npm ls --json printing errors after printing the json (note that sync-exec channels both STDOUT and STDERR and returns the combination).

You should probably use:

const {spawnSync} = require('child_process')
const proc = spawnSync('npm', ['ls', '--json'])
console.log(JSON.parse(proc.stdout.toString()))
// ignore proc.stderr

Erroneous "JSON" output (note STDERR at end):

{
  "name": "gtest",
  "version": "1.0.0",
  "problems": [
    "invalid: [email protected] /Users/me/Desktop/gtest/node_modules/gulp",
    "extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/glob-watcher",
    "extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/undertaker",
    "extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/vinyl-fs",
    "extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/node-pre-gyp"
  ],
  "dependencies": {
    "...": "..."
  }
}
npm ERR! invalid: [email protected] /Users/me/Desktop/gtest/node_modules/gulp
npm ERR! extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/glob-watcher
npm ERR! extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/undertaker
npm ERR! extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/vinyl-fs
npm ERR! extraneous: [email protected] /Users/me/Desktop/gtest/node_modules/node-pre-gyp

Jun 02 '17 16:06 jrop

Thanks, that's super useful!

I'll happily take a PR if you would like to submit

Jun 02 '17 17:06 siddharthkp

This is turning out to be more difficult than I first thought. In my particular case the npm process is exiting before flushing STDOUT, which means that NodeJS gets truncated output back from it. I haven't figured out a workaround for this yet. I am investigating seeing if it is possible to switch to read-package-tree to see if that gives all of the data your utility needs, but the problem with that is that is an asynchronous module, and your code is synchronous. Lots to investigate

Jun 02 '17 21:06 jrop

This seems to be a bug with NPM.

According to NodeJS (nodejs/node/issues/9633) all of STDIO is async, and if the process exits before all the data is flushed, it will not be able to be ready from child_process.

In NPM's lib/utils/error-handler.js file, in exit(code, noLog) -> reallyExit(err) the process is exited explicitly with process.exit(code). If I change that line to process.exitCode = code, then I am able to read all of the child_process's STDOUT.

Jun 02 '17 21:06 jrop

the same issue with npm 5.1.0