<!DOCTYPE html>
<head>
<head>
<meta charset="UTF-8">
<script>
function send(type){
url="http://127.0.0.1:8080/"
xhr=new XMLHttpRequest();
xhr.open("post",url,true);
var data
if(type=="formdata"){
data=new FormData();
data.append("key","value");
}else if(type=="json"){
xhr.setRequestHeader("Content-Type","application/json");
data=JSON.stringify({"key":"value"});
}else if(type=="text"){
data="key=value";
}else if(type=="www"){
xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
data="key=value";
}
xhr.send(data);
}
</script>
</head>
<body>
<div>
<input type="button" onclick="send('formdata')" value="FormData">
<br/>
<input type="button" onclick="send('json')" value="application/json">
<br/>
<input type="button" onclick="send('text')" value="text">
<br/>
<input type="button" onclick="send('www')" value="application/x-www-form-urlencoded">
<div>
</body>
</head>参考：
四种格式：
https://blog.csdn.net/tTU1EvLDeLFq5btqiK/article/details/78734023
转码说明：
https://www.w3schools.com/tags/att_form_enctype.asp