Tuesday, July 4, 2023

Using a site map for generating dynamic menus in web applications

In the last few weeks, I have been playing around with a couple of old and obsolete web applications that I have developed in the past with my own web framework. Much of the functionality that these custom web applications offer are facilitated by my framework, but sometimes these web applications also contain significant chunks custom code.

One of the more interesting features provided by custom code is folding menus (also known as dropdown and dropright menus etc.), that provide a similar experience to the Windows start menu. My guess is that because the start menu experience is so familiar to many users, it remains a frequently used feature by many web applications as of today.

When I still used to actively develop my web framework and many custom web applications (over ten years ago), implementing such a feature heavily relied on JavaScript code. For example, I used the onmouseover attribute on a hyperlink to invoke a JavaScript function that unfolds a panel and the onmouseout attribute to fold a panel again. The onmouseover event handler injects a menu section into the DOM using CSS absolute positioning to put it in the right position on the screen.

I could not use the standard menu rendering functionality of my layout framework, because it deliberately does not rely on the usage of JavaScript. As a consequence, I had to write a custom menu renderer for a web application that requires dynamic menu functionality.

Despite the fact that folding menus are popular and I have implemented them as custom code, I never made it a feature of my layout framework for the following two reasons:

  • I want web applications built around my framework to be as declarative as possible -- this means that I want to concisely express as much as possible what I want to render (a paragraph, an image, a button etc. -- this is something HTML mostly does), rather than specifying in detail how to do it (in JavaScript code). As a result, the usage of JavaScript code in my framework is minimized and non-essential.

    All functionality of the web applications that I developed with my framework must be accessible without JavaScript as much possible.
  • Another property that I appreciate of web technology is the ability to degrade gracefully: the most basic and primary purpose of web applications is to provide information as text.

    Because this property is so important, many non-textual elements, such as an image (img element), provide fallbacks (such as an alt attribute) that simply renders alternative text when graphics capabilities are absent. As a result, it is possible to use more primitive browsers (such as text-oriented browsers) or alternative applications to consume information, such as a text-to-speech system.

    When essential functionality is only exposed as JavaScript code (which more primitive browsers cannot interpret), this property is lost.

Recently, I have discovered that there is a way to implement folding menus that does not rely on the usage of JavaScript.

Moreover, there is also another kind of dynamic menu that has become universally accepted -- the mobile navigation menu (or hamburger menu) making navigation convenient on smaller screens, such as mobile devices.

Because these two types of dynamic menus have become so common, I want to facilitate the implementation of such dynamic menus in my layout framework.

I have found an interesting way to make such use cases possible while retaining the ability to render text and degrade gracefully -- we can use an HTML representation of a site map consisting of a root hyperlink and a nested unordered list as a basis ingredient.

In this blog post, I will explain how implementing these use cases are possible.

The site map feature


As already explained, the basis for implementing these dynamic menus is a textual representation of a site map. Generating site maps is a feature that is already supported by the layout framework:


The above screenshot shows an example page that renders a site map of the entire example web application. In HTML, the site map portion has the following structure:

<a href="/examples/simple/index.php">Home</a>

<ul>
    <li>
        <a href="/examples/simple/index.php/home">Home</a>
    </li>
    <li>
        <a href="/examples/simple/index.php/page1">Page 1</a>
        <ul>
            <li>
                <a href="/examples/simple/index.php/page1/page11">Subpage 1.1</a>
            </li>
            <li>
                <a href="/examples/simple/index.php/page1/page12">Subpage 1.2</a>
            </li>
        </ul>
    </li>
    <li>
        <a href="/examples/simple/index.php/page2">Page 2</a>
        ...
    </li>
    ...
</ul>

The site map, shown in the screenshot and code fragment above, consists of three kinds of links:

  • On top, the root link is displayed that brings the user to the entry page of the web application.
  • The unordered list displays links to all the pages visible in the main menu section that are reachable from the entry page.
  • The nested unordered list displays links to all the pages visible in the sub menu section that are reachable from the selected sub page in the main menu.

With a few simple modifications to my layout framework, I can use a site map as an alternative type of menu section:

  • I have extended the site map generator with the ability to mark selected sub pages and as active, similar to links in menu sections. By adding the active CSS class as an attribute to a hyperlink, a link gets marked as active.
  • I have introduced a SiteMapSection to the layout framework that can be used as a replacement for a MenuSection. A MenuSection displays reachable pages as hyperlinks from a selected page on one level in the page hierarchy, whereas a SiteMap section renders the selected page as a root link and all its visible sub pages and transitive sub pages.

With the following model of a layout:

$application = new Application(
    /* Title */
    "Site map menu website",

    /* CSS stylesheets */
    array("default.css"),

    /* Sections */
    array(
        "header" => new StaticSection("header.php"),
        "menu" => new SiteMapSection(0),
        "contents" => new ContentsSection(true)
    ),

    ...
);

We may render an application with pages that have the following look:


As can be seen in the above screenshot and code fragment, the application layout defines three kinds of sections: a header (a static section displaying a logo), a menu (displaying links to sub pages) and a contents section that displays the content based on the sub page that was selected by the user (in the menu or by opening a URL).

The menu section is displayed as a site map. This site map will be used as the basis for the implementation of the dynamic menus that I have described earlier in this blog post.

Implementing a folding menu


Turning a site map into a folding menu, by using only HTML and CSS, is a relatively straight forward process. To explain the concepts, I can use the following trivial HTML page as a template:


The above page only contains a root link and nested unordered list representing a site map.

In CSS, we can hide the root link and the nested unordered lists by default with the following rules:

/* This rule hides the root link */
body > a
{
    display: none;
}

/* This rule hides nested unordered lists */
ul li ul
{
    display: none;
}

resulting in the following page:


With the following rule, we can make a nested unordered list visible when a user hovers over the surrounding list item:

ul li:hover ul
{
    display: block;
}

Resulting in a web page that behaves as follows:


As can be seen, the unordered list that is placed under the Page 2 link became visible because the user hovers over the surrounding list item.

I can make the menu a bit more fancy if I want to. For example, I can remove the bullet points with the following CSS rule:

ul
{
    list-style-type: none;
    margin: 0;
    padding: 0;
}

I can add borders around the list items to make them appear as buttons:

ul li
{
    border-style: solid;
    border-width: 1px;
    padding: 0.5em;
}

I can horizontally align the buttons by adopting a flexbox layout using the row direction property:

ul
{
    display: flex;
    flex-direction: row;
}

I can position the sub menus right under the buttons of the main menu by using a combination of relative and absolute positioning:

ul li
{
    position: relative;
}

ul li ul
{
    position: absolute;
    top: 2.5em;
    left: 0;
}

Resulting in a menu with the following behaviour:


As can be seen, the trivial example application provides a usable folding menu thanks to the CSS rules that I have described.

In my example application bundled with the layout framework, I have applied all the rules shown above and combined them with the already existing CSS rules, resulting in a web application that behaves as follows:


Displaying a mobile navigation menu


As explained in the introduction, another type of dynamic menu that has been universally accepted is the mobile navigation menu (also known as a hamburger menu). Implementing such a menu, despite its popularity, is challenging IMHO.

Although there seem to be ways to implement such a menu without JavaScript (such as this example using a checkbox) the only proper way to do it IMO is still to use JavaScript. Some browsers have trouble accepting such HTML+CSS-only implementations and it requires the use of an HTML element (an input element) that is not designed for that purpose.

In my example web application, I have implemented a custom JavaScript module, that dynamically transforms a site map (that may have already been displayed as a folding menu) into a mobile navigation menu by performing the following steps:

  • We query the root link of the site map and transform it into a mobile navigation menu button by replacing the text of the root link by an icon image. Clicking on the menu button makes the navigation menu visible or invisible.
  • The first level sub menu becomes visible by adding the CSS class: navmenu_active to the unordered list.
  • The menu button becomes active by adding the CSS class: navmenu_icon_active to the image of the root link.
  • Nested menus can be unfolded or folded. The JavaScript code adds fold icons to each list item of the unordered lists that embed a nested unordered list.
  • Clicking on the fold icon makes the nested unordered list visible or invisible.
  • A nested unordered list becomes visible by adding the CSS class: navsubmenu_active to the unordered list
  • A fold button becomes active by adding the CSS class: navmenu_unfold_active to the fold icon image

It was quite a challenge to implement this JavaScript module, but it does the trick. Moreover, the basis remains a simple HTML-rendered site map that can still be used in text-oriented browsers.

The result of using this JavaScript module is the following navigation menu that has unfoldable sub menus:


Concluding remarks


In this blog post, I have explained a new feature addition to my layout framework: the SiteMapSection that can be used to render menu sections as site maps. Site maps can be used as a basis to implement dynamic menus, such as folding menus and mobile navigation menus.

The benefit of using a site map as a basis ingredient is that a web page still remains useful in its most primitive form: text. As a result, I retain two important requirements of my web framework: declarativity (because a nested unordered list describes concisely what I want) and the ability to degrade gracefully (because it stays useful when it is rendered as text).

Developing folding/navigation menus in the way I described is not something new. There are plenty of examples on the web that show how such features can be developed, such as these W3Schools dropdown menu and mobile navigation menu examples.

Compared to many existing solutions, my approach is somewhat puristic -- I do not abuse HTML elements (such as a check box), I do not rely on using helper elements (such as divs and spans) or helper CSS classes/ids. The only exception is to support dynamic features that are not part of HTML, such as "active links" and the folding/unfolding buttons of the mobile navigation menu.

Although it has become possible to use my framework to implement mobile navigation menus, I still find it sad that I have to rely on JavaScript code to do it properly.

Folding menus, despite their popularity, are nice but the basic one-level menus (that only display a collection of links/buttons of sub pages) are in my opinion fine too and much simpler -- the same implementation is usable on desktops, mobile devices and text-oriented browsers.

With folding menus, I have to test multiple resolutions and devices to check whether they provide the right user experience. Folding menus are useless on mobile devices --- you cannot separately trigger a hover event without generating a click event, making it impossible to unfold a sub menu and peek what is inside.

When it is also desired to provide an optimal mobile device experience, you also need to implement an alternative menu. This requirement makes the implementation of a web application significantly more complex.

Availability


The SiteMapSection has become a new feature of the Java, PHP and JavaScript implementations of my layout framework and can be obtained from my GitHub page.

In addition, I have added a sitemapmenu example web application that displays a site map section in multiple ways:

  • In text mode, it is just displayed as a (textual) site map
  • In graphics mode, when the screen width is 1024 pixels or greater, it displays a horizontal folding menu.
  • In graphics mode, when the screen width is smaller than 1024 pixels and JavaScript is disabled, it displays a vertical folding menu.
  • In graphics mode, when the screen width is smaller than 1024 pixels and JavaScript is enabled, it displays a mobile navigation menu.

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