JavaScript and CSS optimisation

JavaScript and CSS bring your site to life: layouts, menus, sliders, animations. Too much of either slows everything down. Every file has to load before the page is fully usable.

Why JS and CSS affect speed

Heavy scripts and styles slow:

• LCP (Largest Contentful Paint)
• INP (Interaction to Next Paint)
• CLS (Cumulative Layout Shift)
• Overall user experience

Bloated themes and plugin overload are common causes. See Core Web Vitals.

Practical steps

1. Remove unused plugins (WordPress)

Less code means a faster site. Deactivate and delete plugins you don’t use.

2. Choose lightweight themes

Avoid page builders and themes that load many scripts for simple layouts.

3. Question every script

Ask: does this slider, gallery, or animation actually help conversions? If not, consider removing it.

4. Load scripts asynchronously

Non‑critical scripts can load in parallel instead of blocking the page. A developer can help with this.

5. Critical CSS

Inlining the CSS needed for above-the-fold content can speed up initial render. Often handled by caching or optimisation plugins.

6. Font loading

Heavy or poorly loaded fonts block rendering. Use efficient font loading or system fonts where possible.

For Shopify

Shopify loads quickly by default, but themes and apps can add bloat. Remove unused apps, unnecessary animations, and excessive scripts.

Next steps

Optimising JS and CSS often improves speed and Core Web Vitals more than people expect. For the full picture, see Website speed and Image optimisation.