GM.xmlHttpRequest: Received no URL Error - xmlhttprequest

Question

This script is run on a Amazon deals page:
// ==UserScript==
// #name Unnamed Script 138015
// #version 1
//#include http://www.amazon.in/*
// #grant GM_setValue
// #grant GM_getValue
// #grant GM.xmlHttpRequest
// #grant GM_xmlhttpRequest
// #grant GM.addStyle
// #grant GM.getResourceText
// #grant GM.getValue
// #grant GM.setValue
// #grant GM.info
// #require http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js
// ==/UserScript==
var x=document.getElementById("dealTitle"); //fetches the URL
alert(x);
GM.xmlHttpRequest ( {
method: "GET",
url: x,
onload: function (response) {
var parser = new DOMParser ();
var doc = parser.parseFromString (response.responseText, "text/html");
var price = document.getElementsByClassName("a-size-medium a-color-price")[0];
$("body").prepend ('<h1>' + price + '</h1>');
},
onerror: function (e) {
console.error ('**** error ', e);
},
onabort: function (e) {
console.error ('**** abort ', e);
},
ontimeout: function (e) {
console.error ('**** timeout ', e);
}
} );
It shows the following error in the console log.
Error: GM.xmlHttpRequest: Received no URL.
Stack trace:
GM_xmlHttpRequest#user-script:null/Unnamed%20Script%20138015:572:21
userScript#user-script:null/Unnamed%20Script%20138015:504:1
scopeWrapper#user-script:null/Unnamed%20Script%20138015:632:9
#user-script:null/Unnamed%20Script%20138015:487:17
Is there any way to use the link fetched from the page to be sent in the HttpRequest?

Answer 1

getElementById does not return a URL; it returns a node.
The dealTitle element is added via AJAX; it does not exist when your script first runs. So, you need to use AJAX-aware techniques in your script.
Something like this should work:
// ==UserScript==
// #name Unnamed Script 138015
// #version 2
// #match *://www.amazon.in/*
// #grant GM.xmlHttpRequest
// #grant GM_xmlhttpRequest
// #require http://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js
// #require https://gist.github.com/raw/2625891/waitForKeyElements.js
// ==/UserScript==
waitForKeyElements ("#dealTitle", fetchDealPage);
function fetchDealPage (jNode) {
var dURL = jNode.attr ("href");
console.log ("dURL: ", dURL);
GM.xmlHttpRequest ( {
method: "GET",
url: dURL,
//etc...
}
Although you may have to install Tampermonkey, and change the line to GM_xmlhttpRequest ( {.
Not sure GM4 supports using GM.xmlHttpRequest that way.