ajax post request error

Question

<form  id="loginForm" method="post" onsubmit="return false;">
		<div>
			<input type="text" name="userid" id="userid" class="userid" placeholder="id" autocomplete="off" onfocus="" onblur="" /><!-- autocomplete="off" 关闭自动补全 -->
		</div>
		<div>
			<input type="text" name="username" id="username" class="username" placeholder="用户名" autocomplete="off" onfocus="" onblur="" />
		</div>
		<div>
			<input type="password" name="password" id="password" class="password" placeholder="密码" oncontextmenu="return false" onpaste="return false"  />
			<!-- oncontextmenu="return false"关闭右键打开菜单功能 onpaste="return false"关闭粘贴功能 -->
		</div>
		<button id="submit" type="submit" onclick="mysubmit();">登 录</button>
	</form>

表单结构

function mysubmit(){
				var xhr ;

				if (window.XMLHttpRequest)
				{
				    //  IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
				    xhr=new XMLHttpRequest();
				}
				else
				{
				    // IE6, IE5 浏览器执行代码
				    xhr=new ActiveXObject("Microsoft.XMLHTTP");
				}
				xhr.open("POST","http://localhost/graduationProject/server/login.php",true);
				xhr.setRequestHeader("Content-type","application/x-www-form-urlencoded");
				xhr.send("userid=1111&username=1111&password=1111");

		// body...
	}

ajax请求

浏览器报错：index.html:1 Failed to load http://localhost/graduationProject/server/login.php: Redirect from 'http://localhost/graduationProject/server/login.php' to 'http://localhost/graduationProject/browser/flappybirds/index.html' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access.

Answer 1

Cross-domain problem, php adds header('Access-Control-Allow-Origin:*');