code: function open(url, callback){
    var cmd, exec = require('child_process').exec;
    switch(process.platform){
    case 'darwin':
      cmd = 'open';
      break;
    case 'win32':
    case 'win64':
      cmd = 'start ""';//加空的双引号可以打开带有 "&" 的地址
      break;
    case 'cygwin':
      cmd = 'cygstart';
      break;
    default:
      cmd = 'xdg-open';
      break;
    }
    cmd = cmd + ' ' + url + '';
    return exec(cmd, callback);
  }
docs: open a url