Load any file in the browser

browser-x-load.js

///////////////////////////////////////////////////////////////////////////////
//
//  browser_x_loader(tag_name, element_type, callbak[, end_callback])
//
//  Load files in the browser
//
//  Usage:
//
//  <script type="text/x-toni-template" src="tmpl/default.tmpl"></script>
//  <script type="text/x-toni-template" src="tmpl/login.tmpl"></script>
//  <script type="text/x-toni-template" id="test-id">
//    hello templates
//  </script>
//  <script src="js/browser-x-load.js"></script>
//  <script>
//    var templates = []
//    function got_template(src, text) { templates[src] = text }
//    function finished() { alert("Finished!") }
//    browser_x_loader("script", "text/x-toni-template", got_template, finished)
//  </script>
//
//  Author: Toni Homedes i Saun (http://tonihomedes.cat/)
//  License: CC-BY-SA
//
///////////////////////////////////////////////////////////////////////////////
function browser_x_loader(tag_name, element_type, callback, end_callback) {
    "use strict"

    var pending_elements

    function assert(condition, message) {
        if (!condition) {
            throw "Assertion failed" + (message ? ": " + message : "")
        }
    }

    function loadElement(src) {
        var req = new XMLHttpRequest()
        req.open('GET', src, true)
        req.onreadystatechange = function (ev) {
            if (
                req.readyState == 4
                && (req.status == 200 || req.status == 0)
            ) {
                send(src, req.responseText)
            }
        }
        req.overrideMimeType(element_type)
        req.send()
    }

    function addListener(elem, event, listener) {

        assert(elem.addEventListener || elem.attachEvent,
               "What am I supposed to do?")

        if (elem.addEventListener) {
            elem.addEventListener(event, listener, false)
        } else if (elem.attachEvent) {
            elem.attachEvent('on' + event, listener)
        }
    }

    function discount1() {
        assert(pending_elements > 0, "Something is very wrong...")
        --pending_elements
        if (pending_elements === 0 && end_callback) {
            end_callback()
        }

    }
    function send(src, text) {
        callback(src, text)
        discount1()
    }
    function on_load() {
        var i, elements

        elements = document.getElementsByTagName(tag_name)

        pending_elements = 1 // Ghost element to prevent alerts before end
        for (i = 0; i < elements.length; ++i) {
            if (elements[i].getAttribute("type") === element_type) {
                ++pending_elements
                if (typeof elements[i].src === 'string' && elements[i].src !== '') {
                    loadElement(elements[i].src)
                } else {
                    send(elements[i].id, elements[i].text)
                }
            }
        }
        discount1() // Discount ghost
    }

    assert(window, "This does not seem to be a browser...")
    addListener(window, "load", on_load)
}