Get LoginUser details with javascript

/**
* ログインユーザーの管理者フラグの取得
*
*/
function LoginUser() {
    debugger;
    var manageflg = false;
    var loggedInUserId = Xrm.Utility.getGlobalContext().userSettings.userId;
    loggedInUserId = loggedInUserId.replace('{', '').replace('}', '');
    var globalContext = Xrm.Utility.getGlobalContext();
    var globalUrl = globalContext.getClientUrl();
    var req = new XMLHttpRequest();
    req.open("GET", globalUrl + "/api/data/v9.1/systemusers(" + loggedInUserId + ")?$select=new_manage_flg", false);
    req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
    req.setRequestHeader("Accept", "application/json");
    req.setRequestHeader("OData-MaxVersion", "4.0");
    req.setRequestHeader("OData-Version", "4.0");
    req.onreadystatechange = function () {
        if (this.readyState === 4) {
            req.onreadystatechange = null;
            if (this.status === 200) {
                var data = JSON.parse(this.response);
                var userexecutive = data.new_manage_flg;
                if (userexecutive == 1) {
                    executiveflg = true;
                }
            } else {
                Xrm.Utility.alertDialog(this.statusText);
            }
        }
    };
    req.send();

    return manageflg;
}