一、formData向后台传数据<br>
1.formData有set、get、append等方法<br>
1)set():设置数据<br>
var formData=new FormData();<br>
formData.set('a',2);<br>
如果有两个set()方法，且key相同，比如:
formData.set('a',2);
formData.set('a',3);
则返回的是3
2)append():添加数据
var formData=new FormData();
formData.set('a',2);
如果有两个set()方法，且key相同，比如:
formData.set('a',2);
formData.append('a',3);
则返回的是[2,3]
3)get():得到数据
比如通过ajax向后台传数据：
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script>
window.onload=function(){
var oBtn1=document.getElementById('btn1');
oBtn1.onclick=function(){
var xhr=new XMLHttpRequest();
var formData=new FormData();
formData.set('a',12);
xhr.open('post','1.php',true);
xhr.send(formData);
xhr.onreadystatechange=function(){
if(xhr.readyState==4){
if(xhr.status==200){
alert(xhr.responseText);
}else{
alert('失败了')
}
}
}
}
}
</script>
</head>
<body>
<input type="button" name="" value="ajax请求" id="btn1">
</body>
</html>
```
```php
<?php
echo $_POST['a']+$_POST['b'];
?>
```
二、formData文件上传
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<script>
window.onload=function(){
var oBtn=document.getElementById('btn1');
var oF1=document.getElementById('f1');
oBtn.onclick=function(){
var formData=new FormData();
formData.set('f1',oF1);
var xhr=new XMLHttpRequest();
xhr.upload.onload=function(){
console.log('上传成功')
}
xhr.upload.onprogress=function(ev){
console.log(ev.loaded+'/'+ev.total);
}
xhr.open('post','2.php',true);
xhr.send(formData);
xhr.onreadystatechange=function(){
if(xhr.readyState==4){
alert(xhr.status)
}
}
}
}
</script>
</head>
<body>
<input type="file" id="f1">
<input type="button" name="" value="ajax请求" id="btn1">
</body>
</html>
```
0.formData.set('名字', file类型的input)
1.xhr.upload.onload:上传完成
2.xhr.upload.onprogress:进度变化
三、CORS跨域<br>
1.如果是ajax1.0,添加res.setHeader('Access-Control-Allow-Origin','*');即可
```JavasSript
const http=require('http');
let httpServer=http.createServer((req,res)=>{
res.setHeader('Access-Control-Allow-Origin','*');
res.write('aaaa');
res.end();
});
httpServer.listen(8080);
```
2.如果是ajax2.0,需要加上allowHosts.indexOf(req.headers['origin'])!=-1的判断
```JavasSript
const http=require('http');
let allowHosts=['taobao.com','baidu.com'];
let httpServer=http.createServer((req,res)=>{
if(allowHosts.indexOf(req.headers['origin'])!=-1){
res.setHeader('Access-Control-Allow-Origin','*');
}
res.write('aaaa');
res.end();
});
httpServer.listen(8080);
```