参照JQuery中的ajax功能，用原生JS写了一个ajax，功能相对JQuery要少很多，不过基本功能都有，包括JSONP。
调用的方式分为两种：
1. ajax(url, {});
2. ajax({});
调用的方法参照JQuery的ajax，只是 不需要写$.ajax ，只需要写 ajax 就可以了。
代码如下：
!function () {
var jsonp_idx = 1;
var ajax = function (url, options) {
if (typeof url === "object") {
options = url;
url = undefined;
}
var o = {
async: options.async === false ? false : true,
url: url || options.url || '',
data: options.data || null,
type: (options.type || 'POST').toUpperCase(),
dataType: (options.dataType || 'JSON').toUpperCase(), //text,json,jsonp,html,xml
contentType: options.contentType || "application/x-www-form-urlencoded; charset=utf-8",
jsonp: options.jsonp || "callback",
jsonpCallback: options.jsonpCallback || '',
callback: options.callback || options.success || null,
error: options.error || null,
timeout: options.timeout || 4000,
result: ''
};
if (o.dataType === 'JSONP' && o.jsonp !== false) {
return ajaxJSONP(o.url, o.jsonp, o.jsonpCallback, o.callback) || false;
}
if (o.async === true && typeof o.callback !== 'function') {
return false;
}
if (o.dataType === 'HTML' || checkStaticFile(o.url)) {
//由于大多数WEB服务器不允许静态文件响应POST请求（会返回 405 Method Not Allowed），所以改为GET请求
o.type = 'GET';
o.url += (/\?/.test(o.url) ? "&" : "?") + new Date().getTime();
}
var xhr = new XmlHttpRequest();
if (o.async === true) {
xhr.timeout = o.timeout;
}
xhr.open(o.type, o.url, o.async);
xhr.onreadystatechange = function () {
if (4 === xhr.readyState) {
o.result = xhr.responseText;
if (200 === xhr.status) {
switch (o.dataType) {
case 'JSON':
o.result = parseJSON(o.result);
break;
case 'XML':
o.result = parseXML(xhr.responseXML);
break;
}
if (typeof o.callback === 'function') {
o.callback(o.result, xhr.statusText, xhr);
if (o.dataType === 'HTML') {
//执行HTML文件中的JS代码
execScript(o.result);
}
}
} else {
typeof o.error === 'function' ? function () { o.error(o.result, xhr.statusText, xhr); }() : throwError(o.result);
}
xhr = null;
}
};
if ('POST' === o.type) {
xhr.setRequestHeader("content-type", o.contentType);
}
xhr.send(o.data);
if (o.async === false) {
return o.result;
}
};
function XmlHttpRequest() {
return function () {
var len = arguments.length;
for (var i = 0; i < len; i++) {
try { return arguments[i](); } catch (e) { }
}
}(function () { return new XMLHttpRequest() },
function () { return new ActiveXObject('Msxml2.XMLHTTP') },
function () { return new ActiveXObject('Microsoft.XMLHTTP') });
}
function ajaxJSONP(url, jsonp, jsonpCallback, callback) {
//if (!jsonpCallback) {
//不管有没有指定JSONP回调函数，都自动生成回调函数，然后取出数据给ajax回调函数
if (!jsonpCallback || true) {
jsonpCallback = 'jsonpCallback_' + new Date().getTime() + '_' + jsonp_idx++;
window[jsonpCallback] = function (result) {
removeScript(jsonpCallback);
callback(result);
};
}
url += (/\?/.test(url) ? "&" : "?") + jsonp + "=" + jsonpCallback;
return createScript(jsonpCallback, url);
}
function createScript(id, src) {
var obj = document.createElement("script");
obj.id = id;
obj.type = "text/javascript";
obj.src = src;
document.getElementsByTagName("head")[0].appendChild(obj);
return obj;
}
function removeScript(id) {
var script = document.getElementById(id), head = document.getElementsByTagName("head")[0];
if (head && script != null && script.parentNode) {
head.removeChild(script);
}
}
function checkStaticFile(url) {
url = (url || '').split('?')[0];
var ext = url.substr(url.lastIndexOf('.'));
return /(html|htm|txt|json)/ig.test(ext);
}
function execScript(html) {
var ms = html.match(/<script(.|\n)*?>(.|\n|\r\n)*?<\/script>/ig);
if (ms) {
var len = ms.length;
for (var i = 0; i < len; i++) {
var m = ms[i].match(/<script(.|\n)*?>((.|\n|\r\n)*)?<\/script>/im);
if (m[2]) {
if (window.execScript) {
window.execScript(m[2]);
} else {
//window.eval(m[2]);
(function (data) {
return (new Function("return " + data))();
})(m[2].replace(/(^[\s]*)|([\s]*$)/g, ''));
}
}
}
}
}
function throwError(err) {
try {
console.trace();
console.log('data:\r\n\t', err);
} catch (e) { }
throw new Error(err);
}
function parseJSON(data) {
if (typeof data !== "string" || !data) {
return null;
}
if (typeof JSON2 === 'object') {
return JSON2.parse(data);
} else if (typeof JSON === 'object') {
return JSON.parse(data);
} else {
return (new Function("return " + data))();
}
throwError("Invalid JSON: " + data);
}
function parseXML(data) {
if (typeof data !== "string" || !data) {
return null;
}
var xml, tmp;
try {
if (window.DOMParser) { // Standard
tmp = new DOMParser();
xml = tmp.parseFromString(data, "text/xml");
} else { // IE
xml = new ActiveXObject("Microsoft.XMLDOM");
xml.async = "false";
xml.loadXML(data);
}
} catch (e) {
xml = undefined;
}
if (!xml || !xml.documentElement || xml.getElementsByTagName("parsererror").length) {
throwError("Invalid XML: " + data);
}
return xml;
}
window.ajax = ajax;
}();
压缩后的代码：
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