django-htmx-forms

Adding editing capabilities to the frontend in a modern user interface requires the usage of modal forms.

django-htmx-forms is a package which provides tools for working with modal popups, form submission and validation via ajax in a Django project.

I also took the chance to take a closer look at HTMX, a JavaScript framework that handles Ajax communication based on custom HTML attributes.

django-htmx-forms does not require jQuery, nor Bootstrap or other frameworks; HTMX is mostly optional.

Based on my previous somehow incomplete researches as documented here:

• Editing Django models in the front end
• Django Frontend Forms

Installation

Install the package by running:

pip install django-htmx-forms

or:

pip install git+https://github.com/morlandi/django-htmx-forms

In your settings, add:

INSTALLED_APPS = [
    ...
    'htmx_forms',
]

Include library's views mapping (file urls.py):

NOTE: THE FOLLOWING IS NOT REQUIRED NOR POSSIBLE AT THE MOMENT

urlpatterns = [
    ...
    # NOT required, not possible .. yet
    #path('htmx_forms/', include('htmx_forms.urls', namespace='htmx_forms')),
    ...

In your base template, include: the default styles, the javascript support, and optionally the sample HTML template:

<link rel='stylesheet' href="{% static 'htmx_forms.css' %}">
<script src="{% static 'htmx_forms.js' %}"></script>

{% include 'htmx_forms/dialogs.html' %}

Modals with Django

In this context, our main objectives are:

• having a dialog box, to be used as "container" for user interaction, whose layout is coherent with the front-end pages
• the content and life cycle of the dialog can be controlled "server-side"
• the dialog will close when the user has completed or cancelled the operation

The solution suggested by django-htmx-forms requires two actions:

1) provide an HTML template for the dialog layout

2) attach the template to a `HtmxForms.Dialog()` javascript object to control it's behaviour

Since in most cases you will be primarily interested in customizing the modal content only, a default template is provided to render a generic dialog

file: htmx_forms/templates/htmx_forms/dialogs.html:

<div id="dialog_generic" class="dialog draggable">
    <div class="dialog-dialog">
        <div class="dialog-content">
            <div class="dialog-header">
                <span class="spinner">
                    <i class="fa fa-spinner fa-spin"></i>
                </span>
                <span class="close">&times;</span>
                <div class="title">Title</div>
            </div>
            <div class="dialog-body ui-front">
                {% comment %}
                <p>Some text in the dialog ...</p>
                {% endcomment %}
            </div>
            <div class="dialog-footer">
                <input type="submit" value="Close" class="btn btn-close" />
                <input type="submit" value="Save" class="btn btn-save" />
                <div class="text">footer</div>
            </div>
        </div>
    </div>
</div>

When instantiating the javascript HtmxForms.Dialog object, you can select an alternative template instead, providing a suitable value for djalog_selector:

document.addEventListener("DOMContentLoaded", function() {

    dialog1 = new HtmxForms.Dialog({
        dialog_selector: '#dialog_generic',
        html: '<h1>Loading ...</h1>',
        width: '400px',
        min_height: '200px',
        title: '<i class="fa fa-calculator"></i> Select an object ...',
        footer_text: 'testing dialog ...'
    });

});

It is advisable to use an HTML structure similar to the default layout;

Notes:

• adding ".ui-front" to the ".dialog-box" element helps improving the behaviour of the dialog on a mobile client
• adding class ".draggable" makes the Dialog draggable - this is optional, and requires jquery-ui TODO: NEED TO RESTORE THIS WITH VANILLA JS

Opening a Dialog

A static Dialog

The layout of the Dialog is fully determined by the referenced HTML template: either the default "#dialog_generic" of a custom one.

You can further customize the rendering with CSS; the default styles are provided by htmx_forms/static/htmx_forms.css

dialog1 = new HtmxForms.Dialog({
    dialog_selector: '#dialog_generic',
    html: '<h1>Static content goes here ...</h1>',
    width: '600px',
    min_height: '200px',
    title: '<i class="fa fa-calculator"></i> Select an object ...',
    footer_text: 'testing dialog ...',
    enable_trace: true
});

dialog1.open()

A static dialog

A dynamic Dialog

In most cases, you will rather produce the dialog content dynamically.

To obtain that, just add an "url" option to the Djalog constructor, and it will be automatically used to obtain the Dialog content from the server via an Ajax call.

dialog1 = new HtmxForms.Dialog({
    ...
    url: "/some-remote-endpoint/",
    ...

You can obtain the same result within a single HTML tag:

<a href="/some-remote-endpoint/"
   onclick="new HtmxForms.Dialog().open(event); return false;"
   data-html="<h1>Loading ...</h1>"
   data-width="600px"
   data-min-height="200px"
   data-title="<i class='fa fa-calculator'></i> Select an object ..."
   data-button-save-initially-hidden="true"
   data-enable-trace="true"
   >
   Sample dialog ...
</a>

Modal and/or standalone pages

Sometimes it is convenient to reuse the same view to render either a modal dialog, or a standalone HTML page.

This can be easily accomplished providing:

• an "inner" template which renders the content
• an "outer" container template which renders the full page, then includes the "inner" template
• in the view, detect the call context and render one or another

def simple_content2(request):

    try:
        #is_ajax_request = request.accepts("application/json")
        is_ajax_request = request.headers.get('x-requested-with') == 'XMLHttpRequest'
    except AttributeError as e:
        # Django < 4.0
        is_ajax_request = request.is_ajax()

    # Either render only the modal content, or a full standalone page
    if is_ajax_request:
        template_name = 'frontend/includes/simple_content2_inner.html'
    else:
        template_name = 'frontend/includes/simple_content2.html'

    return render(request, template_name, {
    })

here, the "inner" template provides the content; for example:

<div class="row">
    <div class="col-sm-4">
        {% lorem 1 p random %}
    </div>
    <div class="col-sm-4">
        {% lorem 1 p random %}
    </div>
    <div class="col-sm-4">
        {% lorem 1 p random %}
    </div>
</div>

while the "outer" one renders the full page:

{% extends "base.html" %}
{% load static staticfiles i18n %}

{% block content %}
{% include 'frontend/includes/simple_content2_inner.html' %}
{% endblock content %}

Dialog methods

Method	Effects
constructor(options={})	See options list below
open(event=null, show=true)	Open the dialog [1]
close()	Close (hide) the dialog
show()	Make the dialog visible

[1] open():

1. the dialog body will be immediately loaded with static content provided by option "html"
2. then the dialog is shown (unless the "show" parameter is false)
3. then, dynamic content will be loaded from remote address provided by option "url" (if supplied)
4. if successfull, a 'loaded.dialog' event is fired; you can use it to perform any action required after loading

Dialog options

Option	Default value	Notes
dialog_selector	'#dialog_generic'	The selector for HTML dialog template
open_event	null	Used to "remember" the event which triggered Dialog opening and the associated target
html	''	Static content to display in dialog body
url	''	Optional url to retrieve dialog content via Ajax
width	null
min_width	null
max_width	null
height	null
min_height	null
max_height	null
button_save_label	'Save'
button_save_initially_hidden	false	Will be shown after form rendering
button_close_label	'Cancel'
title	''
subtitle	''
footer_text	''
enable_trace	false	show notifications in debug console
callback	null	a callback to receive events
autofocus_first_visible_input	true

Unspecified options will be retrieved from corresponding HTML attributes from the element which fires the dialog opening;

for example:

<a href="{% url 'frontend:whatever' object.id %}"
   data-title="My title"
   data-subtitle="My Subtitle"
   onclick="new HtmxForms.Dialog().open(event); return false;">
        Open
</a>

Option	HTML attribute
url	href
html	data-html
width	data-width
min_width	data-min-width
max_width	data-max-width
height	data-height
min_height	data-min-height
max_height	data-max-height
button_save_label	data-button-save-label
button_close_label	data-button-close-label
title	data-title
subtitle	data-subtitle
footer_text	data-footer-text

Dialog notifications

event_name	params
created	options
closed
initialized
shown
loading	url
loaded	url, data
loading_failed	jqXHR, textStatus, errorThrown
open
submitting	method, url, data
submission_failure	method, url, data
submitted	method, url, data

During it's lifetime, the Dialog will notify all interesting events to the caller, provided he supplies a suitable callback in the contructor:

`self.options.callback(event_name, dialog, params)`

Example:

dialog1 = new HtmxForms.Dialog({
    ...
    callback: function(event_name, dialog, params) {
        console.log('event_name: %o, dialog: %o, params: %o', event_name, dialog, params);
    }
});

Result:

    event_name: "created", dialog: Dialog {options: {…}, element: …}, params: {options: {…}}
    event_name: "initialized", dialog: Dialog {options: {…}, element: …}, params: {}
    event_name: "open", dialog: Dialog {options: {…}, element: …}, params: {}
    event_name: "shown", dialog: Dialog {options: {…}, element: …}, params: {}
    event_name: "loading", dialog: Dialog {options: {…}, element: …}, params: {url: "/admin_ex/popup/"}
    event_name: "loaded", dialog: Dialog {options: {…}, element: …}, params: {url: "/admin_ex/popup/"}
    event_name: "submitting", dialog: Dialog {options: {…}, element: …}, params: {method: "post", url: "/admin_ex/popup/", data: "text=&number=aaa"}
    event_name: "submitted", dialog: Dialog {options: {…}, element: …}, params: {method: "post", url: "/admin_ex/popup/", data: "text=111&number=111"}
    event_name: "closed", dialog: Dialog {options: {…}, element: …}, params: {}

You can also trace all events in the console setting the boolean flag enable_trace.

Forms submission

We've successfully injected data retrieved from the server in our modals, but did not really interact with the user yet.

When the modal body contains a form, things start to become interesting and tricky.

Handling form submission

When a form submission is involved, the modal life cycle has to be modified as follows:

• First and foremost, we need to prevent the form from performing its default submit.

  If not, after submission we'll be redirected to the form action, outside the context of the dialog.

  We'll do this binding to the form's submit event, where we'll serialize the form's content and sent it to the view for validation via an Ajax call.

• Then, upon a successufull response from the server, we'll need to further investigate the HTML received:

  • if it contains any field error, the form did not validate successfully, so we update the modal body with the new form and its errors

  • otherwise, user interaction is completed, and we can finally close the modal

django-htmx-forms already takes care of all these needs automatically, when a form is detected in the content downloaded from the server.

It keeps refreshing the modal after each submission while validation errors are detected, and dismisses it only when the form validation finally succeedes.

Form submission and validation

Implementation

If you're curious, here below is a detailed explanation of how all this is achieved.

Form detection happens after loading the remote content from the server:

... fetch ...

    if (response.ok) {
        ...
        let form = self.element.querySelector('.dialog-content .dialog-body form');
        if (form !== null) {
            // Manage form
            self._form_ajax_submit();
        }
    }

In this case, the code triggers a call to the helper method _form_ajax_submit(), which is the real workhorse.

I developed it adapting the inspiring ideas presented in the brilliant article: Use Django's Class-Based Views with Bootstrap Modals

The full code can found in the source file htmx_forms.js; here below I will briefly summarize a simplified form of the most significant steps.

We start by taking care of the submit button embedded in the form. While it's useful and necessary for the rendering of the form in a standalone page, it's rather disturbing in the modal dialog.

So we look for it in the element conventionally identified by the class form-submit-row, and if found we will hide and replace it with the "Save" button from the modal footer.

// use footer save button, if available
let btn_save = footer.querySelector('.btn-save');
if (self.options.button_save_label !== null && btn_save) {

    let submit_row = form.querySelector('.form-submit-row');
    if (submit_row) {
        submit_row.style.display = 'none';
    }
    self._off(btn_save);
    btn_save = footer.querySelector('.btn-save');

    btn_save.addEventListener('click', function(event) {
        form.requestSubmit();
    });

    btn_save.style.display = 'block';
}

Then, we proceed by hijacking the form submission:

// bind to the form’s submit event
form.addEventListener('submit', function(event) {

    // prevent the form from performing its default submit action
    event.preventDefault();

    // serialize the form’s content and send via an AJAX call
    // using the form’s defined method and action
    let url = form.getAttribute('action') || self.options.url;
    let method = form.getAttribute('method') || 'post';
    let data = new FormData(form);

    let promise = fetch(
        url, {
            method: method,
            body: data,
            mode: 'cors',   // 'no-cors',
            cache: 'no-cache',
            credentials: 'same-origin',
            headers: {
                // make sure request.is_ajax() return True on the server
                'X-Requested-With': 'XMLHttpRequest'
            }
        }
    );
    promise.then(response => {

Finally, we need to detect any form errors after submission, and either repeat the whole process or close the dialog:

...
if (form.querySelectorAll('.has-error').length > 0 || form.querySelectorAll('.errorlist').length > 0) {
    self._form_ajax_submit(true);
} else {
    // otherwise, we've done and can close the modal
    self.close();
}

One last detail: during content loading, we add a "loading" class to the dialog header, to make a spinner icon visible until we're ready to either update or close the modal.

Giving a feedback after successful form submission

Sometimes, you might want to notify the user after successful form submission.

To obtain this, all you have to do, after the form has been validated and saved, is to return an HTML fragment with no forms in it; in this case:

• the popup will not close
• the "save" button will be hidden

thus giving to the user a chance to read your feedback.

Example

In the following example, a form is rendered is a modal and later submitted; form validation will happen as described above.

When the form validates, the user receives a feedback and the modal can be dismissed.

Note that the whole life cycle of the modal is fully controlled by the server.

<a href="/form_submission_example/" onclick="dialog1.open(event); return false;">Form submission and validation ...</a>

<script>
    dialog1 = new HtmxForms.Dialog({
        dialog_selector: '#dialog_generic',
        html: '<h1>Loading ...</h1>',
        width: '400px',
        min_height: '200px',
        title: '<i class="fa fa-calculator"></i> A numeric value is required ...',
        button_save_initially_hidden: true,
        enable_trace: true
    });
</script>

or, equivalently:

<a href="/form_submission_example/"
   onclick="new HtmxForms.Dialog().open(event); return false;"
   data-html="<h1>Loading ...</h1>"
   data-width="400px"
   data-min-height="200px"
   data-title="<i class='fa fa-calculator'></i> A numeric value is required ..."
   data-button-save-initially-hidden="true"
   data-enable-trace="true"
   >
    Form submission and validation ...
</a>

where the url "/form_submission_example/" points to the following view:

def form_submission_example(request):
    if request.method == 'POST':
        form = SimpleForm(data=request.POST)
        if form.is_valid():
            form.save()
            return HttpResponse("<h1>Great !</h1> Your form has been validated")
    else:
        form = SimpleForm()

    return render(request, template_name, {
        'form': form,
    })



class SimpleForm(forms.Form):
    value = forms.IntegerField(required=True, label='value', help_text='Enter a value between 1 and 10')

    def save(self):
        return True

    def clean_value(self):
        value = self.cleaned_data['value']
        if value is not None:
            if value < 1 or value > 10:
                raise forms.ValidationError('This value is not accepteble')
        return value

In the following variation, the same view can be used to render and validate the form both in a modal or in a standalone page:

def form_submission_example(request):
    #is_ajax_request = request.accepts("application/json")
    is_ajax_request = request.headers.get('x-requested-with') == 'XMLHttpRequest'

    # Either render only the modal content, or a full standalone page
    if is_ajax_request:
        template_name = 'htmx_forms/generic_form_inner.html'
    else:
        template_name = 'htmx_forms/generic_form.html'

    if request.method == 'POST':
        form = SimpleForm(data=request.POST)
        if form.is_valid():
            form.save()
            if not is_ajax_request:
                messages.info(request, "Form has been validated")
            else:
                return HttpResponse("<h1>Great !</h1> Your form has been validated")
    else:
        form = SimpleForm()

    return render(request, template_name, {
        'form': form,
    })

Javascript utilities

A few utilities have been included for convenience:

Helper	Purpose
redirect(url, show_overlay=False)	Similar behavior as an HTTP redirect; optionally calls overlay_show('body')
gotourl(url, show_overlay=False)	Similar behavior as clicking on a link; optionally calls overlay_show('body')
reload_page(show_overlay=False)	Reload the current page; optionally calls overlay_show('body')
overlay_show(element)	Show overlay on given element; Requires: {% include 'frontend_forms/overlay.html' %}
overlay_hide(element)	Hide overlay on given element; Requires: {% include 'frontend_forms/overlay.html' %}
hide_mouse_cursor	Hide the mouse cursor
getCookie(name)	Add to POST headers as follows: HtmxForms.getCookie('csrftoken')
adjust_canvas_size(id)	Adapts canvas size to desired size
downloadFromAjaxPost(url, params, headers, callback)	Handle file download from ajax post
display_server_error(errorDetails)	Display an error message; to be refined
display_message(html_content)	Display a message; to be refined

Example:

    dialog1 = new HtmxForms.Dialog({
        html: '<h1>Loading ...</h1>',
        url: '/popup/',
        width: '400px',
        min_height: '200px',
        title: '<i class="fa fa-calculator"></i> Select Object',
        footer_text: 'testing dialog ...',
        enable_trace: true,
        callback: function(event_name, dialog, params) {
            switch (event_name) {
                case "created":
                    console.log('Dialog created: dialog=%o, params=%o', dialog, params);
                    break;
                case "submitted":
                    HtmxForms.reload_page(show_layer=true);
                    break;
            }
        }
    });

HTMX

The solutions discussed so far do not require HTMX.

This is nice, since in some contexts it's convinient to avoid any external dependencies.

Having said this, we will now investigate how HTML can help us in obtaining the same results writing less javascript.

Calling htmx.process() after loading

When you have content that is added to the DOM outside of the normal htmx request cycle but still want htmx attributes to work, you need to explicitly call the Javascript API htmx.process().

This is required for enabling htmx behaviour as explained here: https://htmx.org/api/#process.

At the moment, we do this whenever a loaded event is fired:

    if (event_name === 'loaded') {
        if (typeof htmx !== 'undefined') {
            htmx.process(self.element);
        }
    }

TODO ...

Example: lazy loading

See:

django-htmx-forms/example/frontend/views.py

Line 110 in d09583c

def lazy_loading(request):

Adapted from: https://htmx.org/examples/lazy-load/

Lazy loading

Resources

• Use Django's Class-Based Views with Bootstrap Modals
• How to implement modal popup django forms with bootstrap
• Custom Modal Dialogs
• Modal forms with Django+HTMX
• Modal forms with Django+HTMX (video)
• DiangoTricks: How to Handle Django Forms within Modal Dialogs