Ajax asynchronously retrieves data

[Javascript] functioncreateXHR () {if (typeofXMLHttpRequest! & Quot; undefined & quot;) {returnnewXMLHttpRequest ();} elseif (typeofActiveXObject! & Quot; undefined & quot;) {... [javascript] function createXHR () {if (typeof XMLHttpRequest! = "Undefined") {return new XMLHttpRequest ();} else if (typeof ActiveXObject! = "Undefined") {var version = ["MSXML2.XMLHttp. 6.0 "," MSXML2.XMLHttp. 3.0 "," MSXML2.XMLHttp "]; for (var I = 0; I <version. length; I ++) {try {return new ActiveXObject (version [I]);} catch (e) {// skip} else {throw new Error ("your browser does not support XHR objects! ") ;}// Asynchronous $ (function () {$ (" body "). click (function () {var xhr = createXHR (); xhr. onreadystatechange = function () {if (xhr. readyState = 4) {// determine whether all response data has been received if (xhr. status = 200) {// determines whether a successful alert (xhr. responseText);} else {throw new Error ("An Error occurred while returning data! Status Code: "+ xhr. status +". The status information is: "+ xhr. statusText) ;}} xhr. open (" get "," demo. php? Rand = "+ Math. random (), true); xhr. send (null); // xhr. abort (); // cancel asynchronous request });});