govuk-frontend-html

govuk-frontend-html is a port of govuk-frontend from nunjucks to plain JS functions, with the intention of providing higher performance and more portable implementation which can be used anywhere within node.js and in any templating language that can execute a native JS function.

All of the GOV.UK Design system components have been implemented with a govuk-frontend compatible API, where each function takes the same object parameters as their nunjucks counterpart.

[!IMPORTANT] govuk-frontend-html does not include client side JS or styles, so you will also need to install govuk-frontend.

Installation

npm install govuk-frontend-html

Usage

All GOV.UK Design System components are importable and can be called with an options object to receive an HTML string:

import { govukButton } from 'govuk-frontend-html'

const buttonHtml = govukButton({
  text: 'Start now',
  isStartButton: true
})

console.log(buttonHtml)
// <button type="submit" class="govuk-button govuk-button--start" data-module="govuk-button">
//   Start now
//   <svg class="govuk-button__start-icon" xmlns="http://www.w3.org/2000/svg" width="17.5" height="19" viewBox="0 0 33 40" aria-hidden="true" focusable="false">
//     <path fill="currentColor" d="M0 0h13l20 20-20 20H0l20-20z"/>
//   </svg>
// </button>

Example of a simple fastify server using fastify-html:

import { join } from 'node:path'
import fastifyStatic from '@fastify/static'
import fastify from 'fastify'
import fastifyHtml from 'fastify-html'
import { govukButton, govukTemplate } from 'govuk-frontend-html'

const app = fastify({ logger: true })

app.register(fastifyStatic, {
  root: join(import.meta.dirname, './node_modules/govuk-frontend/dist/govuk/')
})

await app.register(fastifyHtml)

app.addLayout((inner, reply) =>
  govukTemplate({
    assetPath: '/assets',
    headHtml: '<link href="/govuk-frontend.min.css" rel="stylesheet">',
    contentHtml: inner,
    bodyEndHtml: `<script type="module" src="/govuk-frontend.min.js"></script>
  <script type="module">
  import { initAll } from '/govuk-frontend.min.js'
  initAll()
  </script>`
  })
)

app.get('/', async (req, reply) => {
  const startButton = govukButton({
    classes: 'govuk-!-margin-top-2 govuk-!-margin-bottom-8',
    text: 'Start now',
    isStartButton: true
  })

  return reply.html`
    <div class="govuk-grid-row">
      <div class="govuk-grid-column-two-thirds">
        <h1 class="govuk-heading-xl">Apply online for a UK passport</h1>
        <p class="govuk-body">You can apply for, renew, replace or update your passport and pay for it online.</p>
        !${startButton}
      </div>
    </div>
  `
})

await app.listen({ port: 3_000 })

Components

• Accordion
• Back link
• Breadcrumbs
• Button
• Character count
• Checkboxes
• Cookie banner
• Date input
• Details
• Error message
• Error summary
• Exit this page
• Fieldset
• File upload
• Footer
• Header
• Hint
• Input
• Inset text
• Label
• Notification banner
• Pagination
• Panel
• Password input
• Phase banner
• Radios
• Select
• Service navigation
• Skip link
• Summary list
• Table
• Tabs
• Tag
• Task list
• Textarea
• Warning text

Performance

The performance of each component is significantly faster than the govuk-frontend nunjucks alternatives, for example govukButton():

cpu: Apple M1 Pro
runtime: node v22.3.0 (arm64-darwin)

benchmark            time (avg)             (min … max)       p75       p99      p999
------------------------------------------------------- -----------------------------
• govuk-frontend-html
------------------------------------------------------- -----------------------------
start now link      120 ns/iter       (106 ns … 471 ns)    128 ns    159 ns    249 ns
input             93.48 ns/iter     (81.46 ns … 219 ns)    102 ns    126 ns    161 ns
button              161 ns/iter       (142 ns … 348 ns)    170 ns    210 ns    341 ns
with attributes     249 ns/iter       (223 ns … 352 ns)    255 ns    292 ns    310 ns

• nunjucks
------------------------------------------------------- -----------------------------
start now link    5'505 ns/iter   (4'666 ns … 3'417 µs)  5'083 ns 10'042 ns    118 µs
input             5'051 ns/iter   (4'865 ns … 5'398 ns)  5'122 ns  5'327 ns  5'398 ns
button            5'323 ns/iter   (5'111 ns … 5'593 ns)  5'400 ns  5'574 ns  5'593 ns
with attributes   8'346 ns/iter   (8'059 ns … 8'826 ns)  8'460 ns  8'756 ns  8'826 ns