回复内容：ios 上利用后端 js 不执行的特性，加一个心跳机制，判断超时即在后台
var lastfired = new date().gettime();setinterval(function() { now = new date().gettime(); if(now - lastfired > 5000) { // if it's been more than 5 seconds alert(onfocus); } lastfired = now;}, 500);