https://www.union-matematica.org.ar/visibilidad/components/com_extrawatch/js/jdownloadurl.js

1/**
2 * Returns an XMLHttp instance to use for asynchronous
3 * downloading. This method will never throw an exception, but will
4 * return NULL if the browser does not support XmlHttp for any reason.
5 * @return {XMLHttpRequest|Null}
6 */
7function createXmlHttpRequest() {
8    try {
9        if (typeof ActiveXObject != 'undefined') {
10            return new ActiveXObject('Microsoft.XMLHTTP');
11        } else if (window["XMLHttpRequest"]) {
12            return new XMLHttpRequest();
13        }
14    } catch (e) {
15        changeStatus(e);
16    }
17    return null;
18}
19;
20
21
22
23
24
25
26
27
28
29
30/**
31 * This functions wraps XMLHttpRequest open/send function.
32 * It lets you specify a URL and will call the callback if
33 * it gets a status code of 200.
34 * @param {String} url The URL to retrieve
35 * @param {Function} callback The function to call once retrieved.
36 */
37function downloadUrl(url, callback, asText, async) {
38
39if (async == null) {
40	async = true; //asynchronous true by default
41}
42
43    var status = -1;
44    var request = createXmlHttpRequest();
45    if (!request) {
46        return false;
47    }
48
49    request.onreadystatechange = function () {
50        if (request.readyState == 4) {
51            try {
52                status = request.status;
53            } catch (e) {
54                //alert(e);	- suppress 	
55                // Usually indicates request timed out in FF.
56            }
57            if (status == 200) {
58                if (asText == true) {
59                    callback(request.responseText, request.status);
60                } else {
61                    callback(request.responseXML, request.status);
62                }
63                request.onreadystatechange = function () {
64                };
65            }
66        }
67    }
68    request.open('GET', url, async); //using asynchronous loading
69    try {
70        request.send(null);
71    } catch (e) {
72		//suppress errors
73        //changeStatus(e);
74    }
75}
76;
77
78function downloadScript(url) {
79    var script = document.createElement('script');
80    script.src = url;
81    document.body.appendChild(script);
82}