Detailed explanation of the use of native ajax get and post methods

login.onclick = function(){
var xhr = new XMLHttpRequest();
xhr.open("get","http://localhost/ajax2/test2.php?username="+username.value+"&pwd="+pwd2.value,true);
xhr.send();
xhr.onreadystatechange = function(){
if (xhr.readyState == 4) {
if (xhr.status>=200 && xhr.status<300) {
alert(xhr.responseText);
};
};
}
}

btn.onclick = function(){
ajax(
    "GET",
    "http://localhost/ajax2/my02.php",
    {xingming:xingming.value,pwd:pwd.value},
    function(data){
console.log(data);
},
function(errCode){
console.log(errCode);
}
)

var xhr = new XMLHttpRequest();
xhr.open("post","http://localhost/ajax2/login2.php",true);
var data = {
username:username1.value,
pwd:pwd1.value
}
// 设置请求头 告诉服务器发给他的数据是json格式
xhr.setRequestHeader("content-type","application/json");
xhr.send( JSON.stringify(data) );
xhr.onreadystatechange = function(){
if (xhr.readyState == 4) {
if ( xhr.status >= 200 && xhr.status < 300 ) {
alert(xhr.responseText);
};
};
}

var sc = document.createElement("script");
sc.type = "text/javascript";
document.body.appendChild(sc);
sc.src = "http://localhost/ajax2/jsonp.php?cb=myCallBack";
function myCallBack(data){
console.log(data);
}