检索跨浏览器 XmlHttpRequest 的最简单方法

Question

检索适用于所有浏览器的 XmlHttpRequest 对象的最简单和最安全的方法是什么？没有任何额外的库。有没有你经常使用的代码sn-p？

附：我知道网上有很多例子，但这正是我要问的原因：不同的例子太多了，我只想要一些简单且被证明有效的东西。

jQuery 和其他库不是一个选项。 Why does jquery leak memory so badly?

Answer 1

虽然我建议使用完整的库来简化使用，但在现代浏览器中发出 AJAX 请求可能相当简单：

var req = new XMLHttpRequest();
req.onreadystatechange = function(){
    if(this.readyState == 4){
        alert('Status code: ' + this.status);
        // The response content is in this.responseText
    }
}
req.open('GET', '/some-url', true);
req.send();

以下 sn-p 是基于 quirksmode.org 的 sn-p 的更高级的 sn-p，甚至支持非常旧的浏览器（比 Internet Explorer 7 更早）：

function sendRequest(url,callback,postData) {
    var req = createXMLHTTPObject();
    if (!req) return;
    var method = (postData) ? "POST" : "GET";
    req.open(method,url,true);
    // Setting the user agent is not allowed in most modern browsers It was
    // a requirement for some Internet Explorer versions a long time ago.
    // There is no need for this header if you use Internet Explorer 7 or
    // above (or any other browser)
    // req.setRequestHeader('User-Agent','XMLHTTP/1.0');
    if (postData)
        req.setRequestHeader('Content-type','application/x-www-form-urlencoded');
    req.onreadystatechange = function () {
        if (req.readyState != 4) return;
        if (req.status != 200 && req.status != 304) {
//          alert('HTTP error ' + req.status);
            return;
        }
        callback(req);
    }
    if (req.readyState == 4) return;
    req.send(postData);
}

var XMLHttpFactories = [
    function () {return new XMLHttpRequest()},
    function () {return new ActiveXObject("Msxml3.XMLHTTP")},
    function () {return new ActiveXObject("Msxml2.XMLHTTP.6.0")},
    function () {return new ActiveXObject("Msxml2.XMLHTTP.3.0")},
    function () {return new ActiveXObject("Msxml2.XMLHTTP")},
    function () {return new ActiveXObject("Microsoft.XMLHTTP")}
];

function createXMLHTTPObject() {
    var xmlhttp = false;
    for (var i=0;i<XMLHttpFactories.length;i++) {
        try {
            xmlhttp = XMLHttpFactories[i]();
        }
        catch (e) {
            continue;
        }
        break;
    }
    return xmlhttp;
}

Answer 2

不是 100% 确定您的问题 - 但如果您要求函数返回一个跨浏览器 XMLHTTP 实例 - 我们已经在我们的原生 ajax 库中使用了多年 - 在任何浏览器中都不会出现问题

function getXMLHTTP() {
    var alerted;
    var xmlhttp;
    /*@cc_on @*/
    /*@if (@_jscript_version >= 5)
    // JScript gives us Conditional compilation, we can cope with old IE versions.
    try {
        xmlhttp=new ActiveXObject("Msxml2.XMLHTTP")
    } catch (e) {
    try {
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP")
    } catch (E) {
        alert("You must have Microsofts XML parsers available")
    }
    }
    @else
        alert("You must have JScript version 5 or above.")
        xmlhttp=false
        alerted=true
    @end @*/
    if (!xmlhttp && !alerted) {
        // Non ECMAScript Ed. 3 will error here (IE<5 ok), nothing I can
        // realistically do about it, blame the w3c or ECMA for not
        // having a working versioning capability in  <SCRIPT> or
        // ECMAScript.
        try {
            xmlhttp = new XMLHttpRequest();
        } catch (e) {
            alert("You need a browser which supports an XMLHttpRequest Object")
      }
    }
    return xmlhttp
}

Answer 3

根据要求，简单且行之有效：

function Xhr(){ /* returns cross-browser XMLHttpRequest, or null if unable */
    try {
        return new XMLHttpRequest();
    }catch(e){}
    try {
        return new ActiveXObject("Msxml3.XMLHTTP");
    }catch(e){}
    try {
        return new ActiveXObject("Msxml2.XMLHTTP.6.0");
    }catch(e){}
    try {
        return new ActiveXObject("Msxml2.XMLHTTP.3.0");
    }catch(e){}
    try {
        return new ActiveXObject("Msxml2.XMLHTTP");
    }catch(e){}
    try {
        return new ActiveXObject("Microsoft.XMLHTTP");
    }catch(e){}
    return null;
}

将其折叠成一行，我们得到：

function Xhr(){
    try{return new XMLHttpRequest();}catch(e){}try{return new ActiveXObject("Msxml3.XMLHTTP");}catch(e){}try{return new ActiveXObject("Msxml2.XMLHTTP.6.0");}catch(e){}try{return new ActiveXObject("Msxml2.XMLHTTP.3.0");}catch(e){}try{return new ActiveXObject("Msxml2.XMLHTTP");}catch(e){}try{return new ActiveXObject("Microsoft.XMLHTTP");}catch(e){}return null;
}

Answer 4

更简单的方法：

检测 IE：

function detectIE() {
  var ua = window.navigator.userAgent,
   msie = ua.indexOf('MSIE '),
   trident = ua.indexOf('Trident/'),
   edge = ua.indexOf('Edge/');
   if (msie > 0) {return parseInt(ua.substring(msie + 5, ua.indexOf('.', msie)), 10);}
   if (trident > 0) {var rv = ua.indexOf('rv:');return parseInt(ua.substring(rv + 3, ua.indexOf('.', rv)), 10);}
   if (edge > 0) {return parseInt(ua.substring(edge + 5, ua.indexOf('.', edge)), 10);}
   return false;
}

区分 XMLhttp 和 XDomain：

var url = "https://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%27pune%2Cmh%27)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithke"
if (window.XDomainRequest && detectIE()) {
    var xdr = new XDomainRequest();
    xdr.open("GET", url, false);
    xdr.onload = function () {
      var res = JSON.parse(xdr.responseText);
      if (res == null || typeof (res) == 'undefined')
      {
        res = JSON.parse(data.firstChild.textContent);
      }
      publishData(res);
  };
  xdr.send();
} else {
  var xmlhttp = new XMLHttpRequest();
  xmlhttp.onreadystatechange = function() {
  if (xmlhttp.readyState == 4) {
    if (xmlhttp.status == 200 || xmlhttp.status == 304) {
      publishData(JSON.parse(xmlhttp.responseText));
    } else {
      setTimeout(function(){ console.log("Request failed!") }, 0);
    }
  }
}
  xmlhttp.open("GET", url, true);
  xmlhttp.send();
}

function publishData(data){
  console.log(data); //Response
}

完整的例子可以在here找到