<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<script>
function createXHR(){
var xhr=null
let flag=false
var array=[
function a(){return new XMLHttpRequest()},
function b(){throw new ErrorEvent(‘ErrorEvent‘)}
]
for(let i=0;i<array.length;++i){
try{
xhr=array[i]()
createXHR=array[i]
flag=true
break
}catch(e){}
}
if(!flag){
throw new EvalError(‘XMLHttpRequest not supported‘)
}
return xhr
}
var xhr1=createXHR()
var xhr2=createXHR()
console.log(xhr1===xhr2,xhr1,xhr2)
</script>
</body>
</html>
原文：https://www.cnblogs.com/dissipate/p/14639607.html