Easiest way to retrieve cross-browser XmlHttpRequest

What is the easiest and safest way to retrieve XmlHttpRequest object that works across all browsers? Without any extra libraries. Is there a code snippet you use often?

P.S. I know there are tons of examples on the net, but this is precisely the reason I am asking: there are too many different examples, and I just want something simple and proven to work.

jQuery and other libraries i开发者_如何学Cs NOT an option. Why does jquery leak memory so badly?

While I would recommend using a full library to make usage easier, making AJAX requests can be fairly simple in modern browsers:

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();

The following snippet is a more advanced snippet based on a snippet from quirksmode.org and even supports very old browsers (older than Internet Explorer 7):

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;
}

As requested, simple and proven to work:

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;
}

Collapsing it into a single line, we get:

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;
}

not 100% certain of your question - but if you're asking for function to return a cross browser XMLHTTP instance - we have used this in our native ajax library for years - and never a problem in any browser

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
}

A simpler way:

Detect 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;
}

Differentiate XMLhttp and 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
}

Full Example can be found here