原生JS Ajax 请求

var username = document.getElementById('username').value; var password = document.getElementById('password').value; // 第一步：创建对象 var xhr = null; if(window.XMLHttpRequest){ xhr = new XMLHttpRequest(); }else{ xhr = new ActiveXObject("Microsoft.XMLHTTP"); } //初始化 var url = './check.php?username='+username+"&password="+password; xhr.open('post',url,false); //这段代码在xhr.send();执行完之后才能执行 xhr.onreadystatechange = function(){ if(xhr.readyState == 4){ if(xhr.status == 200){ alert(1); var data = xhr.responseText; if(data == 1){ document.getElementById('showInfo').innerHTML = '用户名或者密码错误'; }else if(data == 2){ document.getElementById('showInfo').innerHTML = '登录成功'; } } }; } xhr.send(null);