A brief introduction to ajax
1.ajax native
ajax includes the following steps: 1. Create an AJAX object; 2. Issue an HTTP request; 3. Receive data returned by the server; 4. Update web page data. To summarize, in one sentence, ajax issues an HTTP request through the native XMLHttpRequest object, and then processes the data returned by the server.
Steps:
var xhr = createXHR();//创建对象
xhr.open(“方式”,”地址”,”标志位”);//初始化请求
xhr.setRequestHeader(“”,””);//设置http头信息
xhr.onreadystatechange =function(){}//指定回调函数
xhr.send();//发送请求/ //1.创建xhr对象
var xhr;
if(window.XMLHttpRequest){
xhr = new XMLHttpRequest();
}else{
xhr = new ActiveXObject('Microsoft.XMLHTTP');
}
//异步接受响应
xhr.onreadystatechange = function(){
if(xhr.readyState == 4){
if(xhr.status == 200){
//实际操作
;
}
}
}
//发送请求
xhr.open('get',url,true);
xhr.send();2.jquery encapsulates ajax
$.ajax({
type : "get",
url : '',
dataType : "json",
data:{},
success : function(data){
},error:function(){
console.log('fail');
}
});3.jsonp cross-domain principle
For security reasons , the browser prohibits ajaxcross-domain data acquisition
Step by step demonstration ofscriptsrc Attribute loadingjsFile method to obtain data
Explain the mechanism of cross-domain data acquisition
(1) Dynamic creation scriptTag
(2)Define callback function
(3) Return function call
(4) Pass parameters or global variables
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