我的AJAX代码如下：
data = new FormData();
// data="";
paths = "";
// Create a new HTTP requests, Form data item (data we will send to the server) and an empty string for the file paths.
xhr = new XMLHttpRequest();
// Set how to handle the response text from the server
xhr.onreadystatechange = function(ev){
//console.debug(xhr.responseText);
// console.log("success"+xhr.responseText);
try{
console.log($.parseJSON(xhr.responseText));
var data=$.parseJSON(xhr.responseText);
if(data.success=="yes"){
projectCounter++;
var projectName=$.parseJSON(data.arguments);
console.log(projectName.projectName);
console.log('update table');
if(projectCounter==2){
UploadComplete(projectName.projectName);
}
}
}
catch(e){}
};
// Loop through the file list
for (var i in files){
// Append the current file path to the paths variable (delimited by tripple hash signs - ###)
paths += files[i].webkitRelativePath+"###";
// Append current file to our FormData with the index of i
data.append(i, files[i]);
};
// Append the paths variable to our FormData to be sent to the server
// Currently, As far as I know, HTTP requests do not natively carry the path data
// So we must add it to the request manually.
data.append('paths', paths);
// console.log(paths);
// Open and send HHTP requests to upload.php
xhr.open('POST', "upload.php", true);
console.log(data);
xhr.send(this.data);
我面临的问题是它发送了两次http请求。我收到了2次Http响应。我已经写了console.log（"更新表"），它显示了2次。我很困惑，为什么我收到了2次Http响应，而不是我只发送了1个请求？
您在请求过程中收到多个readyState事件。您希望在这里只在请求完成时收到通知。
用这个扩展你的处理程序：
if(xhr.readyState === 4 //ready) {
}
更新：最初的问题是通过简单的相等性检查（非类型化）解决的，这导致了在一些浏览器中readyState是包含number的string typed field的假设。
if(xhr.readyState == 4 //ready) {
}
您没有在onreadystatechange处理程序中测试readyState。每当状态发生变化时，该函数就会启动。当readyState未完成时，通常会中止函数（通过返回）。
xhr.onreadystatechange = function(ev){
if (this.readyState !== 4) {
return;
}
// ...
我认为问题在于您没有检查xhr的readyState值。onreadystatechange回调代码应该用if语句包装：
if (xhr.readyState === 4) {
// your code here...
}
只有当readyState为4时，请求才真正完成。
谨致问候，Udi