var request = new XMLHttpRequest();    // Emulate the XMLHttpRequest() constructor in IE5 and IE6    if (window.XMLHttpRequest === undefined) {    　　window.XMLHttpRequest = function() {   　　 try {        　　// Use the latest version of the ActiveX object if available        　　return new ActiveXObject("Msxml2.XMLHTTP.6.0");   　　 }catch (e1) {        　　try {    　　　　　　// Otherwise fall back on an older version    　　　　　　return new ActiveXObject("Msxml2.XMLHTTP.3.0");    　　　　} catch(e2) {    　　　　　　// Otherwise, throw an error   　　　　 　　throw new Error("XMLHttpRequest is not supported");    　　　　}    　　}    };}        

function postMessage(msg) {　　var request = new XMLHttpRequest();      // ①New request　　request.open("POST", "/log.php");        // ②POST to a server-side script　　// Send the message, in plain-text, as the request body　　request.setRequestHeader("Content-Type", "text/plain;charset=UTF-8"); //③Request body will be plain text　　request.send(msg);                   // ④Send msg as the request body　　// The request is done. We ignore any response or any error.}

Request.open(“方法”,”URL”);

request.setRequestHeader("Content-Type", "text/plain");

request.send(参数);

// Issue an HTTP GET request for the contents of the specified URL.// When the response arrives successfully, verify that it is plain text// and if so, pass it to the specified callback functionfunction getText(url, callback) {　　var request = new XMLHttpRequest();         // ①Create new request　　request.open("GET", url);                   // ② Specify URL to fetch　　request.onreadystatechange = function() {   // ③Define event listener　　　　// If the request is compete and was successful　　　　if (request.readyState === 4 && request.status === 200) {　　　　var type = request.getResponseHeader("Content-Type");　　　　if (type.match(/^text/))                  // Make sure response is text　　　　　　callback(request.responseText);       // Pass it to callback　　　　}　　};　　request.send(null);         // ④Send the request now}

// Issue a synchronous HTTP GET request for the contents of the specified URL.// Return the response text or throw an error if the request was not successful// or if the response was not text.function getTextSync(url) {　　var request = new XMLHttpRequest();      // Create new request　　request.open("GET", url, false);            // Pass false for synchronous　　request.send(null);                      // Send the request now　　// Throw an error if the request was not 200 OK　　if (request.status !== 200)  throw  new Error(request.statusText);　　// Throw an error if the type was wrong　　var type = request.getResponseHeader("Content-Type");　　if (!type.match(/^text/))   throw new Error("Expected textual response; got: " + type);　　return  request.responseText;}

// Issue an HTTP GET request for the contents of the specified URL.// When the response arrives, pass it to the callback function as a// parsed XML Document object, a JSON-parsed object, or a string.function get(url, callback) {　　var request = new XMLHttpRequest();      // Create new request　　request.open("GET", url);                 // Specify URL to fetch　　request.onreadystatechange = function() {   // Define event listener　　// If the request is compete and was successful　　if (request.readyState === 4 && request.status === 200) {　　　　// Get the type of the response　　　　var type = request.getResponseHeader("Content-Type");　　　　// Check type so we don‘t get HTML documents in the future　　　　if (type.indexOf("xml") !== -1 && request.responseXML){  　　　　　　callback(request.responseXML);               // XML response　　　　}else if (type === "application/json"){　　　　　　// JSON response, 先使用JSON.parse将对象转换为JSON对象　　　　　　callback(JSON.parse(request.responseText));    　　　　}else{　　　　　　callback(request.responseText);               // String response　　　　}　　};　　request.send(null);      // Send the request now}

find=pizza&zipcode=02123&radius=1km

/*** Encode the properties of an object as if they were name/value pairs from  */function encodeFormData(data) {　　if (!data) return "";         // Always return a string　　var pairs = [];             // To hold name=value pairs　　for(var name in data) {     // For each name　　　　if (!data.hasOwnProperty(name))  continue;            // Skip inherited　　　　if (typeof data[name] === "function")  continue;         // Skip methods　　　　var value = http://www.mamicode.com/data[name].toString();                     // Value as string　　　　name = encodeURIComponent(name.replace(" ", "+"));   // Encode name　　　　value = http://www.mamicode.com/encodeURIComponent(value.replace(" ", "+"));   // Encode value　　　　pairs.push(name + "=" + value);                      // Remember name=value pair　　}　　return pairs.join(‘&‘);                 // Return joined pairs separated with &}

function postData(url, data, callback) {　　var request = new XMLHttpRequest();　　request.open("POST", url);                  // POST to the specified url　　request.onreadystatechange = function() {     // Simple event handler　　if (request.readyState === 4 && callback)   // When response is complete　　　　callback(request);                      // call the callback.　　};   　　// Set Content-Type　　request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");  　　request.send(encodeFormData(data));     // Send form-encoded data}

function getData(url, data, callback) {　　var request = new XMLHttpRequest();　　request.open("GET", url + "?" + encodeFormData(data));    // with encoded data added　　request.onreadystatechange = function() {               // Simple event handler　　　　if (request.readyState === 4 && callback)  callback(request);　　};　　request.send(null);                  // Send the request}

function postJSON(url, data, callback) {　　var request = new XMLHttpRequest();　　request.open("POST", url);                   // POST to the specified url　　request.onreadystatechange = function() {     // Simple event handler　　if (request.readyState === 4 && callback)  // When response is complete　　　　callback(request);                     // call the callback.　　};　　request.setRequestHeader("Content-Type", "application/json");　　request.send(JSON.stringify(data));}

// Encode what, where, and radius in an XML document and post them to the// specified url, invoking callback when the response is receivedfunction postQuery(url, what, where, radius, callback) {　　var request = new XMLHttpRequest();　　request.open("POST", url);                  // POST to the specified url　　request.onreadystatechange = function() {     // Simple event handler　　　　if (request.readyState === 4 && callback) callback(request);　　};　　// Create an XML document with root element <query>　　var doc = document.implementation.createDocument("", "query", null);　　var query = doc.documentElement;          // The <query> element　　var find = doc.createElement("find");        // Create a <find> element　　query.appendChild(find);                  // And add it to the <query>　　find.setAttribute("zipcode", where);          // Set attributes on <find>　　find.setAttribute("radius", radius);　　find.appendChild(doc.createTextNode(what));       // And set content of <find>　　// Now send the XML-encoded data to the server.　　// Note that the Content-Type will be automatically set.　　request.send(doc);}

// 查找有data-uploadto 属性的全部<input type="file"> 元素// 并注册onchange handler 事件处理程序//这样任何选择的文件都会自动通过POST方法发送到指定的 "uploadto" URL// 服务器的响应是忽略的whenReady(function() {                                 // Run when the document is ready　　var elts = document.getElementsByTagName("input");      // All input elements　　for(var i = 0; i < elts.length; i++) {                        // Loop through them　　　　var input = elts[i];　　　　if (input.type !== "file")  continue;                  // Skip all but file upload elts　　　　var url = input.getAttribute("data-uploadto");         // Get upload URL　　　　if (!url) continue;                                  // Skip any without a url　　　　input.addEventListener("change", function() {         // When user selects file　　　　　　var file = this.files[0];                          // Assume a single file selection　　　　　　if (!file) return;                               // If no file, do nothing　　　　　　var xhr = new XMLHttpRequest();               // Create a new request　　　　　　xhr.open("POST", url);                         // POST to the URL　　　　　　xhr.send(file);                                // Send the file as body　　　　}, false);　　}});

function postFormData(url, data, callback) {if (typeof FormData =http://www.mamicode.com/=="undefined")   throw new Error("FormData is not implemented");var request = new XMLHttpRequest();               // New HTTP requestrequest.open("POST", url);                        // POST to the specified urlrequest.onreadystatechange = function() {           // A simple event handler.if (request.readyState === 4 && callback)         // When response is completecallback(request);                         // ...call the callback.};var formdata = http://www.mamicode.com/new FormData();for(var name in data) {if (!data.hasOwnProperty(name)) continue;      // Skip inherited propertiesvar value =http://www.mamicode.com/ data[name];if (typeof value =http://www.mamicode.com/=="function")  continue;       // Skip methods// Each property becomes one "part" of the request.// File objects are allowed hereformdata.append(name, value);               // Add name/value as one part}// Send the name/value pairs in a multipart/form-data request body. Each// pair is one part of the request. Note that send automatically sets// the Content-Type header when you pass it a FormData objectrequest.send(formdata);}

Access-Control-Allow-Credentials: true

function createCORSRequest(method, url){　　var xhr = new XMLHttpRequest();　　if (“withCredentials” in xhr){     　　xhr.open(method, url, true);　　} else if (typeof XDomainRequest != “undefined”){　　xhr = new XDomainRequest();　　xhr.open(method, url);　　} else {    　　xhr = null;　　}　　return xhr;}var request = createCORSRequest(“get”, “http://www.somewhere-else.com/page/”);if (request){　　　　request.onload = function(){     　　//do something with request.responseText　　};　　request.send();}

callback({ “name”: “Nicholas” });

回调函数({数据});

// Make a JSONP request to the specified URL and pass the parsed response data to the specified callback. // Add a query parameter named "jsonp" to// the URL to specify the name of the callback function for the request.function getJSONP(url, callback) {　　// Create a unique callback name just for this request　　var cbnum = "cb" + getJSONP.counter++;      // Increment counter each time　　var cbname = "getJSONP." + cbnum;          // As a property of this function　　// Add the callback name to the url query string using form-encoding　　// We use the parameter name "jsonp". Some JSONP-enabled services　　// may require a different parameter name, such as "callback".　　if (url.indexOf("?") === -1)                  // URL doesn‘t already have a query section    　　 url += "?jsonp=" + cbname;            // add parameter as the query section　　else // Otherwise,     　　url += "&jsonp=" + cbname;           // add it as a new parameter.　　// Create the script element that will send this request　　var script = document.createElement("script");　　// Define the callback function that will be invoked by the script　　getJSONP[cbnum] = function(response) {　　try {   　　callback(response);           // Handle the response data　　} finally {                       // Even if callback or response threw an error   　　delete getJSONP[cbnum];      // Delete this function   　　script.parentNode.removeChild(script);             // Remove script　　}};// Now trigger the HTTP requestscript.src = http://www.mamicode.com/url; // Set script urldocument.body.appendChild(script); // Add it to the document}getJSONP.counter = 0;             // A counter we use to create unique callback names

Function loadJSON(url){    var script = document.createElement(“script”);    script.type = “text/javascript”;    script.src =http://www.mamicode.com/ url;    document.getElementsByTagName(“head”)[0].appendChild(script);}