纯Javascript实现ping功能的方法

function ping(ip) {  var img = new Image();  var start = new Date().getTime();  var flag = false;  var isCloseWifi = true;  var hasFinish = false;  img.onload = function() {    if ( !hasFinish ) {      flag = true;      hasFinish = true;      img.src = 'X://';      console.log('Ping ' + ip + ' success. ');    }  };  img.onerror = function() {    if ( !hasFinish ) {      if ( !isCloseWifi ) {        flag = true;        img.src = 'X://';        console.log('Ping ' + ip + ' success. ');      } else {        console.log('network is not working!');      }      hasFinish = true;    }  };  setTimeout(function(){    isCloseWifi = false;    console.log('network is working, start ping...');  },2);  img.src = 'http://' + ip + '/' + start;  var timer = setTimeout(function() {    if ( !flag ) {      hasFinish = true;      img.src = 'X://';      flag = false ;      console.log('Ping ' + ip + ' fail. ');    }  }, 1500);}ping('www.google.com:80');