index.js

const chalk = require('chalk')
const execSync = require('child_process').execSync
const spawn = require('cross-spawn')
const opn = require('opn')

const OSX_CHROME = 'google chrome'

const Actions = Object.freeze({
  NONE: 0,
  BROWSER: 1,
  SCRIPT: 2
})

function getBrowserEnv () {
  const value = process.env.BROWSER
  let action
  if (!value) {
    action = Actions.BROWSER
  } else if (value.toLowerCase().endsWith('.js')) {
    action = Actions.SCRIPT
  } else if (value.toLowerCase() === 'none') {
    action = Actions.NONE
  } else {
    action = Actions.BROWSER
  }
  return {action, value}
}

function executeNodeScript (scriptPath, url) {
  const extraArgs = process.argv.slice(2)
  const child = spawn('node', [scriptPath, ...extraArgs, url], {
    stdio: 'inherit'
  })
  child.on('close', code => {
    if (code === 0) {
      return
    }
    console.log()
    console.log(chalk.red('The script specified as BROWSER environment variable failed.'))
    console.log(chalk.cyan(scriptPath) + ' exited with code ' + code + '.')
    console.log()
  })
  return true
}

function startBrowserProcess (browser, url) {
  // If we're on OS X, the user hasn't specifically
  // requested a different browser, we can try opening
  // Chrome with AppleScript. This lets us reuse an
  // existing tab when possible instead of creating a new one.
  const shouldTryOpenChromeWithAppleScript = process.platform === 'darwin' &&
    (typeof browser !== 'string' || browser === OSX_CHROME)

  if (shouldTryOpenChromeWithAppleScript) {
    try {
      // Try our best to reuse existing tab
      // on OS X Google Chrome with AppleScript
      execSync('ps cax | grep "Google Chrome"')
      execSync('osascript openChrome.applescript "' + encodeURI(url) + '"', {
        cwd: __dirname,
        stdio: 'ignore'
      })
      return true
    } catch (err) {
      // Ignore errors.
    }
  }

  if (process.platform === 'darwin' && browser === 'open') {
    browser = undefined
  }

  // Fallback to opn
  // (It will always open new tab)
  try {
    const options = {app: browser}
    opn(url, options).catch(() => {}) // Prevent `unhandledRejection` error.
    return true
  } catch (err) {
    return false
  }
}

/**
 * Reads the BROWSER evironment variable and decides what to do with it. Returns
 * true if it opened a browser or ran a node.js script, otherwise false.
 */
function openBrowser (url) {
  const {action, value} = getBrowserEnv()
  switch (action) {
    case Actions.NONE:
      return false
    case Actions.SCRIPT:
      return executeNodeScript(value, url)
    case Actions.BROWSER:
      return startBrowserProcess(value, url)
    default:
      throw new Error('Not implemented.')
  }
}

module.exports = openBrowser