Introducing hx-optimistic: Make Your HTMX Apps Feel Instant

HTMX Frontend JavaScript Architecture

Make HTMX apps feel instant with optimistic UI: instant feedback, automatic rollbacks, and no frameworks required, just simple declarative HTML.

Introducing hx-optimistic: Make Your HTMX Apps Feel Instant

Modern web applications feel snappy because they lie to you… in the best possible way. When you click “Like” on a social media post, the heart icon fills immediately, even though the actual request to the server might take hundreds of milliseconds. This technique, called optimistic updates, makes interfaces feel responsive by showing the expected outcome instantly, then quietly handling any errors in the background.

Today, I’m excited to introduce hx-optimistic, an HTMX extension that brings this same instant-feeling magic to hypermedia-driven applications. No complex state management, no heavy JavaScript frameworks, just the declarative simplicity of HTMX with the responsive feel of modern SPAs.

Repo: https://github.com/lorenseanstewart/hx-optimistic

Live demo: https://hx-optimistic-demo-site.vercel.app/

The Problem: HTMX is Great, But Sometimes Feels Slow

HTMX has revolutionized how we build interactive web applications by bringing the power of AJAX directly to HTML. But even the fastest servers introduce network latency. When a user clicks a button and has to wait 200-500ms for visual feedback, the interface feels sluggish compared to client-side frameworks that can update instantly.

Consider this traditional HTMX button:

<button
  hx-post="/api/like"
  hx-target="this"
  hx-swap="outerHTML"
>
  🤍 Like (42)
</button>

While simple and elegant, users must wait for the server response before seeing any change. On slower connections, this could create a frustrating experience.

The Solution: Optimistic Updates, HTMX Style

With hx-optimistic, we can make that same button feel instant:

<body hx-ext="optimistic">
  <button
    hx-post="/api/like"
    hx-target="this"
    hx-swap="outerHTML"
    data-optimistic='{
      "values": {
        "textContent": "❤️ Liked! (43)",
        "className": "btn liked"
      },
      "errorMessage": "Failed to like"
    }'
  >
    🤍 Like (42)
  </button>
</body>

Now when clicked, the button immediately updates to show “❤️ Liked! (43)” while the request happens in the background. If the server confirms the action, the optimistic update becomes permanent. If there’s an error, the button automatically reverts to its original state and shows the error message.

The beauty is in what you don’t need: no state management, no event handlers, no complex JavaScript. Just a declarative configuration that tells hx-optimistic what the success state should look like.

Why Your Users Will Thank You

The difference between a 50ms and 500ms response time isn’t just about speed, it’s also about trust. When users click a button and nothing happens for half a second, they wonder: Did it work? Should I click again? Is the site broken? Loading spinners can mitigate this, but spinners don’t make an app feel snappy and responsive.

With hx-optimistic, every interaction feels instant. Users see their changes immediately, building confidence in your application. This isn’t just about perceived performance; it’s about creating an experience that respects users’ time and intentions.

Real-World Use Cases Where This Matters

E-commerce: Every Millisecond Counts

In e-commerce, hesitation kills conversions. When a user adds an item to their cart, they need immediate confirmation. With traditional server-round-trip approaches, that “Add to Cart” button might feel sluggish, especially on mobile networks. Optimistic updates make the action feel instant, keeping users in their shopping flow.

Admin Dashboards: Fast Inline Actions

Back-office UIs often involve rapid, repetitive actions such as toggling account status, assigning labels, changing order states, or archiving rows. With optimistic updates, badge colors, counts, and button states update immediately, keeping operators in flow while the server processes the change. If the request fails, the UI rolls back automatically and surfaces the error without losing context.

Social Platforms: Engagement Without Friction

Social interactions need to feel effortless. Liking a post, following a user, or saving content should happen at the speed of thought. When these micro-interactions have even small delays, engagement drops. Optimistic updates remove this friction entirely.

Forms and Data Entry: Reducing Cognitive Load

Long forms are already daunting. When each field change requires a server round-trip to validate or save, users feel like they’re fighting the interface. With optimistic updates, inline editing and validation feel smooth, reducing the cognitive burden of data entry.

Check out our live demo to see these patterns in action with working code examples.

Why hx-optimistic is Different

1. Tiny and Fast

At just 3.0KB gzipped, hx-optimistic adds minimal overhead while delivering maximum impact. That’s smaller than most state management libraries (Redux Toolkit (12KB), Zustand (8KB), or MobX (23KB)) while providing a focused solution for optimistic updates.

2. No CSS Required

hx-optimistic ships no CSS. It adds and removes state classes like hx-optimistic and hx-optimistic-error; styling is entirely up to you.

3. Intelligent Error Handling

The extension automatically handles:

  • Automatic rollback on errors
  • Concurrency management (newer requests override older errors)
  • Configurable error display (replace or append error messages)
  • Auto-revert timers for temporary error states

4. Rich Interpolation System

The ${...} syntax supports powerful patterns:

  • ${this.value} - Element’s input value
  • ${textarea} - First textarea in the form
  • ${data:count} - Data attributes
  • ${attr:title} - Any HTML attribute
  • ${status} and ${error} - Error context in error templates

5. Declarative Configuration

Everything is configured via data-optimistic attributes. No JavaScript needed for basic use cases:

{
  "values": { "textContent": "Loading..." },
  "template": "#loading-template",
  "errorMessage": "Request failed",
  "errorMode": "append",
  "delay": 2000
}

The Business Case for Optimistic Updates

Reduced Server Costs

Counter-intuitively, optimistic updates can reduce your infrastructure costs. When users get immediate feedback, they’re less likely to click multiple times, reducing duplicate requests. They’re also more patient with actual processing time since they’ve already seen a response.

Improved Accessibility

Users with slower connections or older devices suffer the most from traditional server-round-trip interactions. Optimistic updates level the playing field, giving all users the same snappy experience regardless of their network conditions. This is especially crucial for international users or those on mobile networks.

Simplified Error Recovery

With hx-optimistic’s automatic rollback, error handling becomes more user-friendly. Instead of leaving users in an uncertain state, the UI intelligently reverts while showing what went wrong. Users maintain context and can retry without losing their place or data.

Progressive Enhancement Done Right

Unlike SPAs that require JavaScript for basic functionality, hx-optimistic enhances existing server-rendered HTML. If JavaScript fails to load, your application still works, it’s just not as snappy. This resilience is crucial for enterprise applications where reliability trumps everything else.

Performance Impact: Making Slow Feel Fast

The psychological impact of optimistic updates is remarkable:

  • Perceived performance improves dramatically, even on fast connections
  • User satisfaction increases because actions feel immediate
  • Error tolerance improves when users see their intent acknowledged instantly

A 500ms server response that feels sluggish becomes imperceptible when the UI updates optimistically.

Getting Started

Add hx-optimistic to your project in seconds:

<script
  defer
  src="https://unpkg.com/htmx.org@2"
></script>
<script
  defer
  src="https://cdn.jsdelivr.net/npm/hx-optimistic@1/hx-optimistic.min.js"
></script>

Enable it globally:

<body hx-ext="optimistic"></body>

Then add data-optimistic to any HTMX element that should feel instant.

The Future of Web Interactions

hx-optimistic represents a new approach to web application UX; one that combines the simplicity of hypermedia with the responsiveness users expect from modern applications. By making optimistic updates accessible through simple HTML attributes, we’re democratizing advanced UX patterns that were previously locked behind complex JavaScript frameworks.

Try our live demo to see hx-optimistic in action, or dive into the documentation to start building more responsive HTMX applications today.

The web is getting faster, one optimistic update at a time. ⚡

hx-optimistic is an open-source project available under the MIT License. Contributions welcome on GitHub.