SimpleUI

Clojure backend for for htmx. Previously known as ctmx.

• Rationale
• Getting started
• Usage
  • component stack
  • ids and values
  • Component Arrays
  • Parameter Casting
  • Additional Parameters
  • Commands
  • Action at a distance (hx-swap-oob)
  • Responses
  • Script Responses
  • Hanging Components
  • Extra hints
• Advanced Usage
• License

Rationale

htmx enables web developers to create powerful webapps without writing any Javascript. Whenever hx-* attributes are included in html the library will update the dom in response to user events. The architecture is simpler and pages load more quickly than in Javascript-oriented webapps.

SimpleUI is a backend accompaniment which makes htmx even easier to use. It works in conjunction with hiccup for rendering and reitit for routing.

Getting started

Getting started is easy with clojure tools and the excellent kit framework.

clojure -Ttools install com.github.seancorfield/clj-new '{:git/tag "v1.2.381"}' :as new
clojure -Tnew create :template io.github.kit-clj :name yourname/guestbook
cd guestbook
make repl

(kit/sync-modules)
(kit/install-module :kit/ctmx)

Quit the process, make repl then

(go)

Visit localhost:3000. To reload changes

(reset)

Usage

First require the library

(require '[simpleui.core :refer :all])

The core of SimpleUI is the defcomponent macro.

(defcomponent ^:endpoint hello [req my-name]
  [:div#hello "Hello " my-name])

This defines an ordinary function which also expands to an endpoint /hello.

To use our endpoint we call make-routes

;; make-routes generates a reitit handler with the root page at /demo
;; and all subcomponents on their own routes
(make-routes
  "/demo"
  (fn [req]
    (page ;; page renders the rest of the page, htmx script etc
      [:div
       [:label "What is your name?"]
       [:input {:name "my-name" :hx-patch "hello" :hx-target "#hello"}]
       (hello req "")])))

Here the only active element is the text input. On the input's default action (blur) it will request to /hello and replace #hello with the server response. We are using hello both as a function and an endpoint. When called as an endpoint arguments are set based on the http parameter my-name.

The first argument to defcomponent is always the req object

component stack

SimpleUI retains a call stack of nested components. This is used to set ids and values in the sections below.

ids and values

In the above example we use a fixed id #hello. If a component exists multiple times you may set id automatically.

[:div.my-component {:id id} ...]

SimpleUI also provides optional path and value functions.

[:input {:type "text" :name (path "first-name") :value (value "first-name")}]
[:input {:type "text" :name (path "last-name") :value (value "last-name")}]

These are unique for each instance of a component and make it easy to retain state over stateless http requests.

Note: path and value only work when id is set at the top level of the component. SimpleUI uses id to record the position of the component in the component stack.

Component Arrays

If you are using the component stack on a page, you must invoke simpleui.rt/map-indexed instead of clojure.core/map. This is because the index of the array forms part of the component stack.

(def data [{:first-name "Fred" :last-name "Smith"}
           {:first-name "Ocean" :last-name "Leader"}])

(defcomponent table-row [req index first-name last-name]
  [:tr ...])

...

[:table
  (rt/map-indexed table-row req data)]

Parameter Casting

htmx submits all parameters as strings. It can be convenient to cast parameters to the required type

(defcomponent my-component [req ^:long int-argument ^:boolean boolean-argument] ...)

You may also cast within the body of defcomponent

[:div
  (if ^:boolean (value "grumpy")
    "Cheer up!"
    "How are you?")]

Casts available include the following

• ^:long Casts to long
• ^:long-option Casts to long (ignores empty string)
• ^:double Casts to double
• ^:double-option Casts to double (ignores empty string)
• ^:longs Casts to array of longs
• ^:doubles Casts to array of doubles
• ^:array Puts into an array
• ^:boolean True when (contains? #{"true" "on"} argument). Useful with checkboxes.
• ^:boolean-true True when (not= argument "false")
• ^:edn Reads string into edn
• ^:keyword Casts to keyword

Additional Parameters

In most cases htmx will supply all required parameters. If you need to include extra ones, set the hx-vals attribute. To serialize the map as json in initial page renders, you should call simpleui.render/walk-attrs on your returned html body (example).

[:button.delete
  {:hx-delete "trash-can"
   :hx-vals {:hard-delete true}}
   "Delete"]

Commands

Commands provide a shorthand to indicate custom actions.

(defcomponent ^:endpoint component [req command]
  (case command
    "print" (print req)
    "save" (save req))
  [:div
    [:button {:hx-post "component:print"} "Print"]
    [:button {:hx-post "component:save"} "Save"]])

command will be bound to the value after the colon in any endpoints.

Action at a distance (hx-swap-oob)

Best to avoid, but sometimes too convenient to resist. htmx provides the hx-swap-oob attribute for updating multiple dom elements within a single response. In SimpleUI we must only provide the additional elements when htmx is updating, not in the initial render

(defcomponent my-component [req]
  (list
    (when top-level?
      [:div.side-element
       {:id (path "path/to/side-element")
        :hx-swap-oob "true"}
        ...])
    [:div.main-element {:id id} ...]))

Be very careful to only include hx-swap-oob elements when top-level? is true.

Responses

By default SimpleUI expects components to return hiccup vectors which are rendered into html.

nil returns http 204 - No Content and htmx will not update the dom.

You may also return an explicit ring map if you wish. A common use case is to refresh the page after an operation is complete

(defcomponent my-component [req]
  (case (:request-method req)
    :post
    (do
      (save-to-db ...)
      simpleui.response/hx-refresh)
    :get ...))

simpleui.response/hx-refresh sets the "HX-Refresh" header to "true" and htmx will refresh the page.

Script Responses

htmx will execute any script tags you include.

[:script "alert('Application successful')"]

You can also mix scripts with visual content.

Hanging Components

If you don't include components in an initial render, reference them as symbols so they are still available as endpoints.

(defcomponent ^:endpoint next-month [req] [:p "next-month"])
(defcomponent ^:endpoint previous-month [req] [:p "previous-month"])

(defcomponent ^:endpoint calendar [req]
              next-month
              previous-month
              [:div#calendar ...])

Extra hints

htmx does not include disabled fields when submitting requests. If you wish to retain state in this case use the following pattern.

[:input {:type "text" :name (path "input") :value (value "input") :disabled disabled?}]
(when disabled?
  [:input {:type "hidden" :name (path "input") :value (value "input")}])

Advanced Usage

SimpleUI makes it possible to build dynamic forms, for details please see advanced usage.

License

Copyright © 2023 Matthew Molloy

This program and the accompanying materials are made available under the terms of the Eclipse Public License 2.0 which is available at http://www.eclipse.org/legal/epl-2.0.

This Source Code may also be made available under the following Secondary Licenses when the conditions for such availability set forth in the Eclipse Public License, v. 2.0 are satisfied: GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version, with the GNU Classpath Exception which is available at https://www.gnu.org/software/classpath/license.html.