htmx Interaction Patterns

Build dynamic interfaces with HTML-over-the-wire — server renders HTML fragments, htmx swaps them in.

Core Concepts

htmx extends HTML with attributes that make AJAX requests and swap content — no JavaScript required.

<!-- Click button → GET /items → replace #item-list content -->
<button hx-get="/items" hx-target="#item-list" hx-swap="innerHTML">
  Load Items
</button>
<div id="item-list"></div>

Key Attributes

Attribute	Purpose	Example
hx-get	GET request	hx-get="/api/items"
hx-post	POST request	hx-post="/api/items"
hx-put	PUT request	hx-put="/api/items/1"
hx-delete	DELETE request	hx-delete="/api/items/1"
hx-target	Where to put response	hx-target="#results"
hx-swap	How to insert	hx-swap="outerHTML"
hx-trigger	When to fire	hx-trigger="click"
hx-indicator	Loading indicator	hx-indicator="#spinner"

Swap Strategies

Strategy	Behavior
innerHTML	Replace children (default)
outerHTML	Replace entire target element
afterbegin	Insert as first child
beforeend	Insert as last child
beforebegin	Insert before target
afterend	Insert after target
delete	Remove target
none	No DOM update

Common Patterns

Search with Debounce

<input type="search" name="q"
  hx-get="/search"
  hx-trigger="input changed delay:300ms"
  hx-target="#results"
  hx-indicator="#search-spinner"
  placeholder="Search skills...">
<span id="search-spinner" class="htmx-indicator">Searching...</span>
<div id="results"></div>

Server returns an HTML fragment:

@app.get("/search")
async def search(q: str = ""):
    results = search_skills(q)
    return HTMLResponse(render_results(results))

Inline Editing

<!-- View mode -->
<div id="skill-42" hx-get="/skills/42/edit" hx-trigger="dblclick" hx-swap="outerHTML">
  <h3>testing-patterns</h3>
  <p>Write effective tests across the stack...</p>
</div>

<!-- Edit mode (returned by server) -->
<form id="skill-42" hx-put="/skills/42" hx-swap="outerHTML">
  <input name="name" value="testing-patterns">
  <textarea name="description">Write effective tests...</textarea>
  <button type="submit">Save</button>
  <button hx-get="/skills/42" hx-swap="outerHTML">Cancel</button>
</form>

Infinite Scroll

<div id="item-list">
  <!-- Items rendered here -->
  <div hx-get="/items?page=2"
       hx-trigger="revealed"
       hx-swap="outerHTML">
    Loading more...
  </div>
</div>

Server returns items + next trigger:

<div class="item">Item 11</div>
<div class="item">Item 12</div>
<!-- Next page trigger -->
<div hx-get="/items?page=3" hx-trigger="revealed" hx-swap="outerHTML">
  Loading more...
</div>

Lazy Loading

<div hx-get="/dashboard/metrics" hx-trigger="load" hx-swap="innerHTML">
  <div class="skeleton-loader"></div>
</div>

Active Search with URL State

<input type="search" name="q"
  hx-get="/search"
  hx-trigger="input changed delay:300ms"
  hx-target="#results"
  hx-push-url="true">

Confirmation Dialogs

<button hx-delete="/items/42"
        hx-confirm="Delete this item?"
        hx-target="#item-42"
        hx-swap="outerHTML swap:500ms">
  Delete
</button>

Server-Sent Events

<div hx-ext="sse" sse-connect="/events" sse-swap="message">
  Waiting for updates...
</div>

from sse_starlette.sse import EventSourceResponse

@app.get("/events")
async def events():
    async def generate():
        while True:
            data = await get_update()
            yield {"data": render_update(data)}
    return EventSourceResponse(generate())

Server-Side Patterns

Partial vs Full Responses

@app.get("/items")
async def list_items(request: Request):
    items = await get_items()
    if "HX-Request" in request.headers:
        # htmx request: return fragment
        return HTMLResponse(render_items_fragment(items))
    else:
        # Normal request: return full page
        return HTMLResponse(render_full_page(items))

Response Headers

from starlette.responses import HTMLResponse

@app.post("/items")
async def create_item(request: Request):
    item = await save_item(request)
    response = HTMLResponse(render_item(item))
    response.headers["HX-Trigger"] = "itemCreated"  # Client-side event
    response.headers["HX-Retarget"] = "#item-list"
    response.headers["HX-Reswap"] = "afterbegin"
    return response

OOB (Out-of-Band) Swaps

Update multiple elements from one response:

<!-- Primary swap -->
<div id="item-42">Updated item content</div>
<!-- OOB: also update the counter -->
<span id="item-count" hx-swap-oob="true">43 items</span>

CSS Integration

/* Loading indicator */
.htmx-indicator { opacity: 0; transition: opacity 200ms; }
.htmx-request .htmx-indicator { opacity: 1; }

/* Settling animation */
.htmx-settling { opacity: 0; }
.htmx-settled { opacity: 1; transition: opacity 300ms; }

/* Added items */
.htmx-added { opacity: 0; }
.htmx-settled.htmx-added { opacity: 1; transition: opacity 300ms; }

Anti-Patterns

• Returning JSON from htmx endpoints — Always return rendered HTML fragments
• Large page replacements — Return small, targeted fragments
• No loading indicators — Always show feedback during requests
• Ignoring non-htmx requests — Support full-page loads for bookmarkability
• Client-side state management — Keep state on the server; let HTML be the state