Thursday, October 11, 2018

little-elements webapp shell

I recently updated to use unbundled javascript modules to load custom elements and style rules. It worked great, except I soon noticed that initial page load would present an un-styled, no-custom-element rendering of the page until the javascript modules finished loading asynchronously... ugh.

I worked around the problem by implementing a simple application shell. The html pages under now extend a compile-time nunjucks template, basicShell.html.njk (npm install @littleware/little-elements). The shell hides the page content with a style rule, maybe loads the webcomponentsjs polyfill, and renders a "Loading ..." message if the main.js javascript module doesn't load fast enough. I also extended the main javascript module on each page to signal the shell when it has finished rendering the initial page content. For example - indexMain.js for looks like this:

import './headerSimple/headerSimple.js';

if ( window['littleShell'] ) {

The index.html nunjucks template looks like this:

{% extends "little-elements/lib/styleGuide/shell/basicShell.html.njk" %}

{% block head %}
{% endblock %}

{% block content %}
    <lw-header-simple title="Home">
   <script src="{{ jsroot }}/@littleware/little-apps/lib/indexMain.js" type="module"></script>
{% endblock %}

A visitor to may now briefly see a "Loading" screen for the first page load, but subsequent page loads generally load fast enough from cache that the shell doesn't bother to show the "Loading" screen. I can improve on this by extending the shell with a service worker - that will be my next project.

I envy gmail's loading screen that renders a crazy animation of a googley envelope. Fancy!