Custom Gutenberg blocks, REST API work, and the interaction performance work that decides whether your site passes Core Web Vitals. Written to survive the next WordPress update.
A WordPress JavaScript developer builds custom Gutenberg blocks in React, wires the front end to the REST API, and fixes the script problems that cause failing Core Web Vitals and console errors. I have worked on WordPress for 7+ years across 250+ projects, and most work is quoted at a fixed price within 48 hours of a call.
JavaScript is the part of a WordPress site that most often gets worse over time without anyone deciding to make it worse. Every plugin brings its own scripts. Every marketing tool adds a tag. A page builder ships a bundle sized for every feature it offers rather than the three you use. None of it is a mistake individually, and together it is why a site that launched fast feels sluggish two years later.
A WordPress JavaScript developer is who you call at that point, or earlier if you need something the plugin directory does not have. The work splits cleanly in two. There is building: custom blocks, REST-driven interfaces, interactive features. And there is subtraction: working out what is loading, what it costs, and what can go.
The second half gets underrated. Google’s Interaction to Next Paint metric, which replaced First Input Delay in March 2024, measures responsiveness across a whole visit rather than the first tap. Long JavaScript tasks on the main thread are the usual cause of a failing score, and you cannot minify your way out of code that should not be running.
Blocks are the other half. WordPress chose React for the editor, and the Block Editor Handbook documents that surface properly. Custom blocks written against it survive core updates. Blocks assembled by copying a tutorial from 2019 do not, which is why so much block code breaks at every major release.
Six kinds of work that cover most JavaScript engagements on a WordPress site.
Blocks built in React with locked layouts your editors cannot break, structured attributes instead of pasted markup, and a server-side render where SEO matters more than editor preview fidelity.
Filtering, search, load-more and form flows that update without a page reload. Custom endpoints with proper permission callbacks and nonces, rather than an admin-ajax handler open to the world.
INP work: breaking up long tasks, removing script that blocks the main thread, and cutting the payload page builders ship on pages that use none of it.
Chat widgets, tag managers, pixels and embeds loaded on interaction or behind a facade, so a tool you use twice a week stops costing every visitor.
Console errors, plugins fighting over jQuery versions, scripts loading in the wrong order, and interactions that work on desktop and fail on an actual phone.
Calculators, configurators, filtered directories and multi-step forms, written in vanilla JavaScript where a framework would be weight for its own sake.
Related service pages: custom plugin development, Core Web Vitals optimization, and bug fixing.
If more than two of these are true, the JavaScript on your site is costing you more than fixing it would.
Send me the URL. I will run it against real field data, tell you which scripts are costing you the score, and say plainly whether it is a configuration fix or a build job.
Get a Free Script AuditFour principles that shape every JavaScript engagement I take on.
Lab scores are useful for finding problems and useless for judging severity. A page that scores 60 in Lighthouse on a throttled connection may be fine for your actual visitors, and a page that scores 90 may be failing INP in the field because the score never measured the interaction people actually perform.
So the starting point is field data from the Chrome UX Report where enough traffic exists, and a mid-range Android where it does not. That decides whether there is a problem worth paying to solve, and which page has it.
The fastest script is the one that does not load. Before anyone minifies, defers or bundles anything, the question is which scripts belong on this page at all. A slider library on a page without a slider, an animation library for an effect nobody scrolls to, three plugins each loading their own date picker: all of it is common and all of it is deletable.
Conditional loading follows. WordPress gives you a script loader with dependencies and per-page control for exactly this reason, and most plugins ignore it and enqueue globally. Fixing that is often worth more than every other optimisation combined. Deeper work lives on the speed optimization page.
Custom blocks break at major releases for one reason: they were built against something WordPress never promised to keep. A selector lifted from a theme, a global a plugin happened to expose, an internal function that was never public.
Blocks written against the documented block API survive. They also behave in the editor the way editors expect, which matters more than it sounds, because a block your team finds confusing gets worked around rather than used. That works alongside a custom theme or on top of Elementor, depending on how your site is built.
Suppressing a console error is not fixing it. Neither is loading a script later until the race condition stops appearing, which works until traffic or a slower connection makes it appear again.
Every fix comes with a short note on what caused it. That matters because plugin conflicts recur: the same two plugins will fight again after the next update, and a note saying which ones and why turns a half-day of rediscovery into a ten-minute fix. Ongoing cover through maintenance plans.
Four ways to engage, depending on whether you need something built, something fixed, or a score moved.
| Model | Suits | How it works | Typical timeline |
|---|---|---|---|
| Fixed-price build | A defined block set or feature | Quote within 48 hours after the discovery call, scope written down | Most builds |
| Debugging job | Something throws errors or behaves oddly | Diagnosis first, quoted per job | Often resolved same week |
| Performance sprint | Failing INP or a JavaScript-heavy page | Audit, then a prioritised fix list | 1 to 2 weeks |
| White-label partnership | Agencies needing block or JS capacity | Under your brand, direct with your PM | Recurring overflow work |
Most work is quoted fixed-price, so you know the number before anything begins.
Custom blocks, INP and Core Web Vitals, framework choices, jQuery, headless, and third-party scripts.
Free 30-minute call. Tell me what you need built or what is throwing errors, and you get a fixed-price quote within 48 hours after the discovery call. If a plugin would do the job, I will say so.
