Global (tenant scoped) HTML/JS 'web part' framework for SharePoint Online

AJAXFrames.js

// replacement function for console.log(), which avoids 'undefined' exception in IE 8
window.LogMsg = function (msg) {
    if (window.console) {
        console.log(msg);
    }
};

// set up root namespaces
window.LS = window.LS || {};
LS.AJAXFrames = LS.AJAXFrames || {};

LS.AJAXFrames.Init = function () {
    // don't load the content when the page is in edit mode
    if (document.forms[MSOWebPartPageFormName].MSOLayout_InDesignMode.value == 0) {
        // check for newly loaded ajax-iframe divs twice per second (as these can be loaded/added to the page after this JS file is loaded)
        setInterval(function () {
            jQuery('.ajax-iframe').each(function () {
                var element = jQuery(this);
                var frameUrl = encodeURI(element.attr('data-src'));
                LogMsg("Loading ajax frame " + frameUrl);
                
                // show loading message
                element.html("<span style='border: 1px solid #eee; margin-top: 10px; padding: 10px; display:inline-block;'><img src='_layouts/images/loading.gif' style='vertical-align:bottom; width:16px; height:16px;' /> Loading...</span>");

                jQuery.ajax({
                    url: frameUrl,
                    cache: false,
                    async: true,
                    dataType: "html"
                }).done(function (data) {
                    setTimeout(function () {
                        element.html(data);
                    }, 1000); // show the loading message for at least a second before adding the HTML to the <div>, as this looks nicer
                }).fail(function(request, status, err) { LogMsg([request, status, err]); });

                element.removeClass('ajax-iframe'); // load the content once, then remove the class (to prevent loading multiple times)
            });
        }, 500);
    }
};
_spBodyOnLoadFunctionNames.push("LS.AJAXFrames.Init"); // don't execute the function until SharePoint is ready

AJAXFrames_ScriptEditorWebPart.xml

<WebPartPages:ScriptEditorWebPart
	runat="server"
	Content="&lt;div class=&quot;ajax-iframe&quot; data-src=&quot;/sites/assets/Style Library/HTML/SiteList.html&quot;&gt;&lt;/div&gt;"
	ChromeType="TitleOnly"
	Description="Displays a list of all site collections in the tenant that the current user has access to."
	Title="Site List"
	ID="g_89b95591_10e3_4ff9_a4a3_5a5b0a6c9e7f"
	WebPart="true"
	partorder="2">
	</WebPartPages:ScriptEditorWebPart>