Optimization: Reduce JavaScript execution time

[rfultz]

Background

Looking to optimize the site's performance and that of the homepage specifically, the Lighthouse tool in Chromium browsers has made some suggestions. Some of these will have repercussions throughout the app so we're going to make them their own tickets.

Recommendation: Reduce JavaScript execution time

Consider reducing the time spent parsing, compiling, and executing JS. You may find delivering smaller JS payloads helps with this. details

Overview

We could speed our page load and render by a few seconds by optimizing our JS files.

Benefit (the 80 of 80/20)

Moderate

Effort (the 20 of 80/20)

Minimal to significant
Could be less noticeable after removing JS files that aren't used, inlining some, and deferring others. May be alleviated with a new build routine (with Webpack 4+)

Complications

• With no 'done' state, this could become an optimization time sink
• Should make sure we don't remove code from pages where it's needed

Related tickets

• Preload key requests
• Remove unused JavaScript
• Remove unused CSS
• Preconnect to required origins
• Eliminate render-blocking resources
• Ensure text remains visible during webfont load
• Reduce the impact of third-party code
• Does not use passive listeners to improve scrolling performance
• Image elements do not have explicit width and height
• Serve static assets with an efficient cache policy
• Minimize main-thread work
• Avoid an excessive DOM size
• Avoid enormous network payloads
• [aria-hidden="true"] elements contain focusable descendents
• Elements with an ARIA [role] that require children to contain a specific [role] are missing some or all of those required children
• [aria-*] attributes do not have valid values
• ARIA IDs are not unique
• Lists do not contain only
• elements and script supporting elements (<script> and )
• [user-scalable="no"] is used in the element or the [maximum-scale] attribute is less than 5
• Links to cross-origin destinations are unsafe
• Serves images with low resolution