index.js

var https = require('https')
var semver = require('semver')
var debug = require('debug')('npm-versions')

module.exports = function () {
  var headers = {
    'accept': 'application/json',
    'accept-encoding': 'identity',
    'user-agent': 'https://github.com/github-utils/npm-versions',
  }
  
  return function* versions(repo) {
    var res = yield function (done) {
      https.request({
        method: 'GET',
        host: 'registry.npmjs.org',
        path: '/' + repo,
        headers: headers,
        agent: false,
      })
      .on('error', done)
      .on('response', done.bind(null, null))
      .end()
    }

    debug('%s got status code %s', repo, res.statusCode)

    if (res.statusCode !== 200) {
      res.destroy()
      throw new Error('failed to get npmjs.org/' + repo + '\'s versions.')
    }

    var body = yield function (done) {
      var buf = ''
      res.setEncoding('utf8')
      res.on('data', function (chunk) {
        buf += chunk
      })
      res.once('end', function () {
        done(null, buf)
      })
    }

    return Object.keys(JSON.parse(body).versions)
      .filter(valid)
      .sort(semver.rcompare)
  }
}

function valid(x) {
  return semver.valid(x)
}