openBrowser.js

'use strict';

const execSync = require('child_process').execSync;
const spawn = require('cross-spawn');
const color = require('colors-cli');
const opn = require('opn');

// https://github.com/sindresorhus/opn#app
var OSX_CHROME = 'google chrome';

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

function getBrowserEnv() {
  // Attempt to honor this environment variable.
  // It is specific to the operating system.
  // See https://github.com/sindresorhus/opn#app for documentation.
  const value = process.env.BROWSER;
  let action;
  if (!value) {
    // Default.
    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) {
      console.log();
      console.log(color.red('The script specified as BROWSER environment variable failed.'));
      console.log(String(scriptPath).cyan + ' exited with code ' + code + '.');
      console.log();
      return;
    }
  });
  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.
    }
  }

  // Another special case: on OS X, check if BROWSER has been set to "open".
  // In this case, instead of passing `open` to `opn` (which won't work),
  // just ignore it (thus ensuring the intended behavior, i.e. opening the system browser):
  // https://github.com/facebookincubator/create-react-app/pull/1690#issuecomment-283518768
  if (process.platform === 'darwin' && browser === 'open') {
    browser = undefined;
  }

  // Fallback to opn
  // (It will always open new tab)
  try {
    var 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:
      // Special case: BROWSER="none" will prevent opening completely.
      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;