原生JavaScript判断是否移动设备

function isMobile(){
  if (typeof this._isMobile === 'boolean'){
    return this._isMobile;
  }
  var screenWidth = this.getScreenWidth();
  var fixViewPortsExperiment = rendererModel.runningExperiments.FixViewport || rendererModel.runningExperiments.fixviewport;
  var fixViewPortsExperimentRunning = fixViewPortsExperiment && (fixViewPortsExperiment.toLowerCase() === "new");
  if(!fixViewPortsExperiment){
    if(!this.isAppleMobileDevice()){
      screenWidth = screenWidth/window.devicePixelRatio;
    }
  }
  var isMobileScreenSize = screenWidth < 600;
  var isMobileUserAgent = false;
  this._isMobile = isMobileScreenSize && this.isTouchScreen();
  return this._isMobile;
}