JS获取url参数,JS发送json格式的POST请求方法

<script type="text/javascript">

function US() {var name, value;var str = location.href;var num = str.indexOf("?");str = str.substr(num + 1);var arr = str.split("&");for (var i = 0; i < arr.length; i++) {num = arr[i].indexOf("=");if (num > 0) {name = arr[i].substring(0, num);value = arr[i].substr(num + 1);this[name] = value;}}}

var us = new US();var xhr = new XMLHttpRequest();xhr.open("POST", "/searchguard/api/v1/auth/login", true);xhr.setRequestHeader("Content-type", "application/json");xhr.setRequestHeader("kbn-version", "5.3.0");xhr.onreadystatechange = function() {if (xhr.readyState == 4) {if (xhr.status == 200) {window.location.href = us.nextUrl;}}};xhr.send(JSON.stringify({"username" : us.u,"password" : us.p}));</script>