Init SharePoint RequestExecutor

spRequestExecutor.js

 $(document).ready(function () {
    var hostweburl;
    var appweburl;

    //Get the URI decoded URLs.
    hostweburl = decodeURIComponent( getQueryStringParameter("SPHostUrl") );
    appweburl = decodeURIComponent( getQueryStringParameter("SPAppWebUrl") );

    // Load the .js files using jQuery's getScript function.
    $.getScript(
    hostweburl + "/_layouts/15/SP.RequestExecutor.js",
    continueExecution
    );

    // After the cross-domain library is loaded, execution
    // continues to this function.
    function continueExecution() {
    var executor;

    // Initialize your RequestExecutor object.
    executor = new SP.RequestExecutor(appweburl);
    // You can issue requests here using the executeAsync method
    // of the RequestExecutor object.
    }

    // Function to retrieve a query string value.
    function getQueryStringParameter(paramToRetrieve) {
    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] == paramToRetrieve)
    return singleParam[1];
    }
    }
    });