Avoiding Front-End SPOF in Single Page Apps

3 minute read Published

Effective mitigation of common single points of failure in web applications.
This post originally appeared on the Trunk Club Tech Blog. Some links have been updated to point to their new canonical resource locations.

A couple years back Steve Souders gave a great talk at Fluent Conf titled Your Script Just Killed My Site (video). During the talk Steve explained front-end SPOF and pointed towards a nice tool for detecting it. Fast-forward a couple of years and front-end SPOF is still a concern in web development. And, when building a single-page app, SPOF is an even bigger deal as it can cause an entire web app to become unresponsive, putting users at the mercy of the browser to download and execute 3rd-party scripts prior to bootstrapping. Read on to learn how to avoid front-end SPOF using Trunk Club’s single-page app skeleton, Brunch with Panache (BWP).

Learn how to avoid front-end SPOF using Trunk Club’s single-page app skeleton, Brunch with Panache

Avoiding front-end SPOF in a single-page app like those created with BWP is relatively simple, but often flies in the face of what 3rd parties suggest in their implementation guides. Here’s the typical site integration approach advocated by many 3rd parties, even today:

  1. Insert our script into the HEAD or BODY of your main template. We should be first. Or last.
  2. Don’t worry, our response times are really, really fast.
  3. And we’re using a script-loader with, ajax so everything will be fast.

I’ve seen this approach advocated for a slew of products including Google Analytics, Typekit, BrightTag, Test and Target, Bazaarvoice, and it’s very misleading. If you’re dropping a SCRIPT tag into your template markup, and the DOMContentLoaded event hasn’t fired yet, you’re primed for SPOF. I’ve seen tiny script-loaders cause upwards of 20 second page load times. There’s a better way.

If you’re building a single-page app the solution is simple, wait until the app begins to initialize before calling scripts, and call them all in a non-blocking manner from the application’s own JS.

To avoid SPOF in BWP single-page applications, simply do the following:

  • For each script with an href attribute, move the URL provided to initialize.coffee and load them asynchronously. If using jQuery or Zepto, this can be done using $.getScript and $.get, respectively. If you’re not using either of those libraries simply build or borrow something similar to load the files in a non-blocking fashion.
  • For any script that runs a script-loader, embed that code into initialize.coffee and you’re all set.

If you experience any issues with browsers that are not evergreen like Chrome and Firefox just ask the magic StackOverflow, or look into browser quirks (no, I’m not referring to IE’s venerable quirks mode).

Below is a sample of the initialize.coffee file used in one of our major production applications at Trunk Club, showing how we load our analytics provider as well as web fonts:

'use strict'

utils = require('lib/utils')

initialize = ->

  # Add Analytics for tracking with Segment.io
  `
  window.analytics||(window.analytics=[]),window.analytics.methods=["identify","track","trackLink","trackForm","trackClick","trackSubmit","page","pageview","ab","alias","ready","group","on","once","off"],window.analytics.factory=function(a){return function(){var t=Array.prototype.slice.call(arguments);return t.unshift(a),window.analytics.push(t),window.analytics}};for(var i=0;i<window.analytics.methods.length;i++){var method=window.analytics.methods[i];window.analytics[method]=window.analytics.factory(method)}window.analytics.load=function(a){var t=document.createElement("script");t.type="text/javascript",t.async=!0,t.src=("https:"===document.location.protocol?"https://":"http://")+"d2dq2ahtl5zl1z.cloudfront.net/analytics.js/v1/"+a+"/analytics.min.js";var n=document.getElementsByTagName("script")[0];n.parentNode.insertBefore(t,n)},window.analytics.SNIPPET_VERSION="2.0.6",
  window.analytics.load(utils.app.regexes.origin.prod.test(window.location.hostname) ? "44yg1der8p" : "moz42de0rp");
  `

  # Add Typekit for web font support
  `
  (function(d) {
    var config = {
      kitId: 'led3rp',
      scriptTimeout: 3000
    },
    h=d.documentElement,t=setTimeout(function(){h.className=h.className.replace(/\bwf-loading\b/g,"")+" wf-inactive";},config.scriptTimeout),tk=d.createElement("script"),f=false,s=d.getElementsByTagName("script")[0],a;h.className+=" wf-loading";tk.src='//use.typekit.net/'+config.kitId+'.js';tk.async=true;tk.onload=tk.onreadystatechange=function(){a=this.readyState;if(f||a&&a!="complete"&&a!="loaded")return;f=true;clearTimeout(t);try{Typekit.load(config)}catch(e){}};s.parentNode.insertBefore(tk,s)
  })(document);
  `

  # Add Davy promises if available and we are using Exoskeleton
  if Backbone.Deferred and Davy?
    Backbone.Deferred = ->
      new Davy

  # Start application
  Application = require('application')
  new Application

# Initialize the application on DOM ready event.
# Use jQuery if available. Otherwise use native.
if $?
  $(document).ready(initialize)
else
  document.addEventListener('DOMContentLoaded', initialize)

Tip: Don’t forget to add the 'use strict' as shown above to enforce strict mode on the embedded JS.

And if you’ve enabled CoffeeLint (you are linting, aren’t you?), you can omit linting of initialize.coffee by updating the `brunch-config.js` with a negative-lookahead assertion like so:

plugins: {
  coffeelint: {
    pattern: /^app\/(?!initialize).*\.coffee$/
  }
}

Questions? Just let us know.

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