SharePoint Add-in with REST API call Visual Studio 2017 with SharePoint Online

SharePoint Add-in with REST API call - SharePoint Online
-Visual Studio 2017.

To connect Rest API- App should needed the permission- try add app permissions in AppManifest.xml  (I have added Site Collection with Full rights).

var appUrl;

    var hostWebUrl;

    // Reading the query string from the URL

    function getQueryStringParameter(param) {

        var params = document.URL.split("?")[1].split("&");

        var strParams = "";

        for (var i = 0; i < params.length; i = i + 1) {

            var singleParam = params[i].split("=");

            if (singleParam[0] == param) {

                return singleParam[1];

            }

        }

    }

    $(document).ready(function () {

        appUrl = decodeURIComponent(getQueryStringParameter("SPAppWebUrl"));

        hostWebUrl = decodeURIComponent(getQueryStringParameter("SPHostUrl"));

        //cross domain library

        $.getScript(hostWebUrl + "/_layouts/15/SP.RequestExecutor.js", connectREST);

    });

    function connectREST() {

        var url = appUrl + "/_api/SP.AppContextSite(@target)/web/lists/getbytitle('Change Request')/items?@target='" + hostWebUrl + "'";

        var executor = new SP.RequestExecutor(appUrl);

        executor.executeAsync({

            url: url,

            method: "GET",

            headers: { "Accept": "application/json;odata=verbose" },

            success: function (data) {

                $("#message").html("REST call connected/success");

            },

            error: function (data) {

                $("#message").html("Error while REST API");

            }

        });

    }