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A TeuxDeux clone in plain HTML, CSS and JavaScript (no build steps). It's fully animated and runs smoothly at 60 FPS with a total transfer size of 50KB (unminified).

Try it online →

More importantly, it's a case study showing that vanilla web development is viable in terms of maintainability, and worthwhile in terms of user experience (50% less time to load and 90% less bandwidth in this case).

There's no custom framework invented here. Instead, the case study was designed to discover minimum viable patterns that are truly vanilla. The result is maintainable, albeit verbose and with considerable duplication.

If anything, the case study validates the value of build steps and frameworks, but also demonstrates that standard web technologies can be used effectively and there are only a few critical areas where a vanilla approach is clearly inferior.

Intermediate understanding of the web platform is required to follow through.

Table of Contents

1. Motivation

I believe too little has been invested in researching practical, scalable methods for building web applications without third party dependencies.

It's not enough to describe how to create DOM nodes or how to toggle a class without a framework. It's also rather harmful to write an article saying you don't need library X, and then proceed in describing how to roll your own untested, inferior version of X.

What's missing are thorough examples of complex web applications built only with standard web technologies, covering as many aspects of the development process as possible.

This case study is an attempt to fill this gap, at least a little bit, and inspire further research in the area.

2. Method

The method for this case study is as follows:

  • Pick an interesting subject.
  • Implement it using only standard web technologies.
  • Document techniques and patterns found during the process.
  • Assess the results by common quality standards.

This section describes the method in more detail.

2.1. Subject

I've chosen to build a functionally equivalent clone of TeuxDeux for this study. The user interface has interesting challenges, in particular performant drag & drop when combined with animations.

The original TeuxDeux app deserves praise here. In my opinion it has the best over-all concept and UX of all the to-do apps out there. Thank you!

The user interface is arguably small (which is good for a case study) but large enough to require thought on its architecture.

However, it is lacking in some key areas:

  • Routing
  • Asynchronous resource requests
  • Server-side rendering

2.2. Rules

To produce valid vanilla solutions, and because constraints spark creativity, I came up with a set of rules to follow throughout the process:

  • Only use standard web technologies.
  • Only use widely supported JS features unless they can be polyfilled (1).
  • No runtime JS dependencies (except polyfills).
  • No build steps.
  • No general-purpose utility functions related to the DOM/UI (2).

(1) This is a moving target; the current version is using ES2020.

(2) These usually end up becoming a custom micro-framework, thereby questioning why you didn't use one of the established and tested libraries/frameworks in the first place.

2.3. Goals

The results are going to be assessed by three major concerns:

2.3.1. User Experience

The resulting product should be comparable to or better than the original regarding functionality, performance and design.

This includes testing major browsers and devices.

2.3.2. Code Quality

The resulting implementation should adhere to established code quality standards in the industry.

This will be difficult to assess objectively, as we will see later.

2.3.3. Generality of Patterns

The discovered techniques and patterns should be applicable in a wide range of scenarios.

3. Implementation

This section walks through the resulting implementation, highlighting techniques and problems found during the process. You're encouraged to inspect the source code alongside this section.

3.1. Basic Structure

Since build steps are ruled out, the codebase is organized around plain HTML, CSS and JS files. The HTML and CSS mostly follows rscss (devised by Rico Sta. Cruz) which yields an intuitive, component-oriented structure.

The stylesheets are slightly verbose. I missed SCSS here and I think one of these is a must-have for bigger projects. Additionally, the global CSS namespace problem is unaddressed (see e.g. CSS Modules).

All JavaScript files are ES modules (import/export).

Basic code quality (code style, linting) is guided by Prettier, stylelint and ESLint. I've set the ESLint parser to ES5 to ensure only ES5 code is allowed.

Note that I've opted out of web components completely. I can't clearly articulate what I dislike about them but I never missed them throughout this study.

The basic structure comes with some boilerplate, e.g. referencing all the individual stylesheets and scripts from the HTML; probably enough to justify a simple build step.

It is otherwise straight-forward and trivial to understand (literally just a bunch of HTML, CSS and JS files).

3.2. JavaScript Architecture

Naturally, the JavaScript architecture is the most interesting part of this study.

I found that using a combination of functions, query selectors and DOM events is sufficient to build a scalable, maintainable codebase, albeit with some trade-offs as we will see later.

Conceptually, the proposed architecture loosely maps CSS selectors to JS functions which are mounted (i.e. called) once per matching element. This yields a simple mental model and synergizes with the DOM and styles:

.todo-list -> TodoList

.app-collapsible -> AppCollapsible


This proved to be a useful, repeatable pattern throughout all of the implementation process.

3.2.1. Mount Functions

Mount functions take a DOM element as their (only) argument. Their responsibility is to set up initial state, event listeners, and provide behavior and rendering for the target element.

Here's a "Hello, World!" example of mount functions:

// define mount function
// loosely mapped to ".hello-world"
export function HelloWorld(el) {
  // define initial state
  const state = {
    title: 'Hello, World!',
    description: 'An example vanilla component',
    counter: 0,

  // set rigid base HTML
  el.innerHTML = `
    <h1 class="title"></h1>
    <p class="description"></p>
    <div class="my-counter"></div>

  // mount sub-components

  // attach event listeners
  el.addEventListener('modifyCounter', (e) =>
    update({ counter: state.counter + e.detail })

  // initial update

  // define idempotent update function
  function update(next) {
    // update state
    // optionally optimize, e.g. bail out if state hasn't changed
    Object.assign(state, next);

    // update own HTML
    el.querySelector('.title').innerText = state.title;
    el.querySelector('.description').innerText = state.description;

    // pass data to sub-scomponents
      new CustomEvent('updateMyCounter', {
        detail: { value: state.counter },

// define another component
// loosely mapped to ".my-counter"
export function MyCounter(el) {
  // define initial state
  const state = {
    value: 0,

  // set rigid base HTML
  el.innerHTML = `
      <span class="value"></span>
      <button class="increment">Increment</button>
      <button class="decrement">Decrement</button>

  // attach event listeners
  el.querySelector('.increment').addEventListener('click', () => {
    // dispatch an action
    // use .detail to transport data
      new CustomEvent('modifyCounter', {
        detail: 1,
        bubbles: true,

  el.querySelector('.decrement').addEventListener('click', () => {
    // dispatch an action
    // use .detail to transport data
      new CustomEvent('modifyCounter', {
        detail: -1,
        bubbles: true,

  el.addEventListener('updateMyCounter', (e) => update(e.detail));

  // define idempotent update function
  function update(next) {
    Object.assign(state, next);

    el.querySelector('.value').innerText = state.value;

// mount HelloWorld component(s)
// any <div class="hello-world"></div> in the document will be mounted

This comes with quite some boilerplate but has useful properties, as we will see in the following sections.

Note that any part of a mount function is entirely optional. For example, a mount function does not have to set any base HTML, and may instead only set event listeners to enable some behavior.

Also note that an element can be mounted with multiple mount functions. For example, to-do items are mounted with TodoItem and AppDraggable.

Compared to React components, mount functions provide interesting flexibility as components and behaviors can be implemented using the same idiom and combined arbitrarily.


3.2.2. Data Flow

I found it effective to implement one-way data flow similar to React's approach, however exclusively using custom DOM events.

  • Data flows downwards from parent components to child components through custom DOM events.
  • Actions flow upwards through custom DOM events (bubbling up), usually resulting in some parent component state change which is in turn propagated downwards through data events.

The data store is factored into a separate behavior (TodoStore). It only receives and dispatches events and encapsulates all of the data logic.

Listening to and dispatching events is slightly verbose with standard APIs and certainly justifies introducing helpers. I didn't need event delegation à la jQuery for this study but I believe it's a useful concept that is difficult to do concisely with standard APIs.


3.2.3. Rendering

Naively re-rendering a whole component using .innerHTML should be avoided as this may hurt performance and will likely break important functionality which browsers have already been optimizing for decades:

  • <a>, <button>, <input>, etc. may lose focus.
  • Form inputs may lose data.
  • Text selection may be reset.
  • CSS transitions may not work correctly.
  • Event listeners may need to be reattached.

As seen in 3.2.1., rendering is therefore split into some rigid base HTML and an idempotent, complete update function which only makes necessary changes.

  • Idempotency is key here, i.e. update functions may be called at any time and should always render the component correctly.
  • Completeness is equally important, i.e. update functions should render the whole component, regardless of what triggered an update.

In effect, this means almost all DOM manipulation is done in update functions, which greatly contributes to robustness and readability of the codebase.

As seen above this approach is quite verbose and ugly compared to JSX, for example. However, it's very performant and can be further optimized by checking for data changes, caching selectors, etc. It is also simple to understand.


3.2.4. Reconciliation

Expectedly, the hardest part of the study was rendering a variable amount of dynamic components efficiently. Here's a commented example from the implementation outlining the reconciliation algorithm:

export function TodoList(el) {
  const state = {
    items: [],

  el.innerHTML = `<div class="items"></div>`;

  el.addEventListener('updateTodoList', (e) => update(e.detail));

  function update(next) {
    Object.assign(state, next);

    const container = el.querySelector('.items');

    // mark current children for removal
    const obsolete = new Set(container.children);

    // map current children by data-key
    const childrenByKey = new Map();

    obsolete.forEach((child) =>
      childrenByKey.set(child.getAttribute('data-key'), child)

    // build new list of child elements from data
    const children = => {
      // find existing child by data-key
      let child = childrenByKey.get(;

      if (child) {
        // if child exists, keep it
      } else {
        // otherwise, create new child
        child = document.createElement('div');

        // set data-key

        // mount component

      // update child
        new CustomEvent('updateTodoItem', { detail: { item: item } })

      return child;

    // remove obsolete children
    obsolete.forEach((child) => container.removeChild(child));

    // (re-)insert new list of children
    children.forEach((child, index) => {
      if (child !== container.children[index]) {
        container.insertBefore(child, container.children[index]);

It's very verbose and has lots of opportunity to introduce bugs. Compared to a simple loop in JSX, this seems insane. It is quite performant as it does minimal work but is otherwise messy; definitely a candidate for a utility function or library.

3.3. Drag & Drop

Implementing drag & drop from scratch was challenging, especially regarding browser/device consistency.

Using a library would have been a lot more cost-effective initially. However, having a customized implementation paid off once I started introducing animations as both had to be coordinated closely. I can imagine this would have been a difficult problem when using third party code for either.

The drag & drop implementation is (again) based on DOM events and integrates well with the remaining architecture. It's clearly the most complex part of the study but I was able to implement it without changing existing code besides mounting behaviors and adding event handlers.

I suspect the drag & drop implementation to have some subtle problems on touch devices, as I haven't extensively tested them. Using a library for identifying the gestures could be more sensible and would reduce costs in testing browsers and devices.


3.4. Animations

For the final product I wanted smooth animations for most user interactions. This is a cross-cutting concern which was implemented using the FLIP technique as devised by Paul Lewis.

Implementing FLIP animations without a large refactoring was the biggest challenge of this case study, especially in combination with drag & drop. After days of work I was able to implement the algorithm in isolation and coordinate it with other concerns at the application's root level. The useCapture mode of addEventListener proved to be very useful in this case.


4. Testing


5. Assessment

5.1. User Experience

Most important features from the original TeuxDeux application are implemented and usable:

  • Daily to-do lists
  • Add/edit/delete to-do items
  • Custom to-do lists
  • Add/edit/delete custom to-do lists
  • Drag & drop to-do items across lists
  • Reorder custom to-do lists via drag & drop
  • Local Storage persistence

Additionally, most interactions are smoothly animated at 60 frames per second. In particular, dragging and dropping gives proper visual feedback when elements are reordered.

The latter was an improvement over the original application when I started working on the case study in 2019. In the meantime, the TeuxDeux team released an update with a much better drag & drop experience. Great job!

One notable missing feature is Markdown support. It would be insensible to implement Markdown from scratch; this is a valid candidate for using an external library as it is entirely orthogonal to the remaining codebase.

The application has been tested on latest Chrome, Firefox, Safari, and Safari on iOS.

TODO Test more browsers and devices.

A fresh load of the original TeuxDeux application transfers around 500 KB and finishes loading at over 1000 ms, sometimes up to 2000ms (measured in 05/2022). Reloads finish at around 500ms.

With a transferred size of around 50 KB, the vanilla application consistently loads in 300-500 ms—not minified and with each script, stylesheet and icon served as an individual file. Reloads finish at 100-200ms; again, not optimized at all (with e.g. asset hashing/indefinite caching).

To be fair, my implementation misses quite a few features from the original. I suspect a fully equivalent clone to be well below 100 KB transfer, though.

TODO Run more formal performance tests and add figures for the results.

5.2. Code Quality

Unfortunately, it is quite hard to find undisputed, objective measurements for code quality (besides trivialities like code style, linting, etc.). The only generally accepted assessment seems to be peer reviewal.

To have at least some degree of assessment of the code's quality, the following sections summarize relevant facts about the codebase and some opinionated statements based on my experience in the industry.

5.2.1. The Good

  • No build steps
  • No external dependencies at runtime besides polyfills
    • No dependency maintenance
    • No breaking changes to monitor
  • Used only standard technologies:
    • Plain HTML, CSS and JavaScript
    • Standard DOM APIs
  • Very few concepts introduced:
    • Mount functions (loosely mapped by CSS class names)
    • State separated from the DOM
    • Idempotent updates
    • Data flow using custom events
  • Compare the proposed architecture to the API/conceptual surface of Angular or React...
  • Progressive developer experience
    • Markup, style, and behavior are orthogonal and can be developed separately.
    • Adding behavior has little impact on the markup besides adding classes.
  • Debugging is straight-forward using modern browser developer tools.
  • The app can be naturally enhanced from the outside by handling/dispatching events (just like you can naturally animate some existing HTML).
  • Little indirection
  • Low coupling
  • The result is literally just a bunch of HTML, CSS, and JS files.

All source files (HTML, CSS and JS) combine to under 2400 lines of code, including comments and empty lines.

For comparison, prettifying the original TeuxDeux's minified JS application bundle yields 52678 LOC (05/2022).

To be fair, my implementation misses quite a few features from the original. I suspect a fully equivalent clone to be well below 10000 LOC, though.

5.2.2. The Verbose

  • Stylesheets are a bit verbose. SCSS would help here.
  • Simple components require quite some boilerplate code.
  • el.querySelectorAll(':scope ...') is somewhat default/expected and would justify a helper.
  • Listening to and dispatching events is slightly verbose.
  • Although not used in this study, event delegation is not trivial to implement without code duplication.

Eliminating verbosities through build steps and a minimal set of helpers would reduce the comparably low code size (see above) even further.

5.2.3. The Bad

  • Class names share a global namespace.
  • Event names share a global namespace.
    • Especially problematic for events that bubble up.
  • No code completion in HTML strings.
  • The separation between base HTML and dynamic rendering is not ideal when compared to JSX, for example.
  • JSX/virtual DOM techniques provide much better development ergonomics.
  • Reconciliation is verbose, brittle and repetitive. I wouldn't recommend the proposed technique without a well-tested helper function, at least.
  • You have to remember mounting behaviors correctly when creating new elements. It would be helpful to automate this somehow, e.g. watch elements of selector X (at all times) and ensure the desired behaviors are mounted once on them.
  • No type safety. I've always been a proponent of dynamic languages but since TypeScript's type system provides the best of both worlds, I cannot recommend using it enough.
  • We're effectively locked out of using NPM dependencies that don't provide browser-ready builds (ES modules or UMD).
  • Most frameworks handle a lot of browser inconsistencies for free and continuously monitor regressions with extensive test suites. The cost of browser testing is surely a lot higher when using a vanilla approach.

Besides the issues described above, I believe the codebase is well organized and there are clear paths for bugfixes and feature development. Since there's no third party code, bugs are easy to find and fix, and there are no dependency limitations to work around.

A certain degree of DOM API knowledge is required but I believe this should be a goal for any web developer.

5.3. Generality of Patterns

Assessing the generality of the discovered techniques objectively is not really possible without production usage. From my experience, however, I can't imagine any scenario where mount functions, event-based data flow etc. are not applicable. The underlying principles power the established frameworks, after all:

  • State is separated from the DOM (React, Angular, Vue).
  • Rendering is idempotent and complete (React's pure render function).
  • One-way data flow (React)

An open question is if these patterns hold for library authors. Although not considered during the study, some observations can be made:

  • The JavaScript itself would be fine to share as ES modules.
  • However, event naming needs great care, as dispatching (bubbling) events from imported behaviors can trigger parent listeners in consumer code.
    • Can be mitigated by providing options to prefix or map event names.
  • CSS names share a global namespace and need to be managed as well.
    • Could be mitigated by prefixing as well, however making the JavaScript a bit more complex.

6. Conclusion

The result of this study is a working todo application with decent UI/UX and most of the functionality of the original TeuxDeux app, built using only standard web technologies. It comes with better overall performance at a fraction of the code size and bandwidth.

The codebase seems manageable through a handful of simple concepts, although it is quite verbose and even messy in some areas. This could be mitigated by a small number of helper functions and simple build steps (e.g. SCSS and TypeScript).

The study's method helped discovering patterns and techniques that are at least on par with a framework-based approach for the given subject, without diverging into building a custom framework.

A notable exception to the latter is rendering variable numbers of elements in a concise way. I was unable to eliminate the verbosity involved in basic but efficient reconciliation. Further research is needed in this area, but for now this appears to be a valid candidate for a (possibly external) general-purpose utility.

When looking at the downsides, remember that all of the individual parts are self-contained, highly decoupled, portable, and congruent to the web platform. The resulting implementation cannot "rust", by definition, as no dependencies can become out of date.

Another thought to be taken with a grain of salt: I believe frameworks make simple tasks even simpler, but hard tasks (e.g. implementing cross-cutting concerns or performance optimizations) often more difficult.

Setting some constraints up-front forced me to challenge my assumptions and preconceptions about vanilla web development. It was quite liberating to avoid general-purpose utilities and get things done with what's readily available.

As detailed in the assessment, the study would likely be more convincing if build steps were allowed. Modern JavaScript and SCSS could reduce most of the unnecessarily verbose parts to a minimum.

Finally, this case study does not question using dependencies or frameworks in general—they do provide lots of value in many areas. It was a constrained experiment designed to discover novel methods for vanilla web development and, hopefully, inspire innovation and further research in the area.

7. What's Next?

I'd love to hear feedback and ideas on any aspect of the case study. It's still lacking in some important areas, e.g. testing techniques.

Pull requests, questions, and bug reports are more than welcome!

Here are a few ideas I'd like to see explored in the future:

  • Run another case study with TypeScript, SCSS, and build steps (seems promising).
  • Research validation rules for utility functions and external dependencies.
  • Experiment with architectures based on virtual DOM rendering and standard DOM events.
  • Compile discovered rules, patterns and techniques into a comprehensive guide.

Case studies constrained by a set of formal rules are an effective way to find new patterns and techniques in a wide range of domains. I'd love to see similar experiments in the future.

8. Appendix

8.1. Links

General resources I've used extensively:

Useful articles regarding FLIP animations:

Projects I've inspected for drag & drop architecture:

8.2. Response



9. Changelog


  • Small improvements
  • Fix date seeking bug on Safari


  • Refactored for ES2020
  • Refactored for event-driven communication exclusively
  • Moved original ES5-based version of the study to /es5
  • Added assessment regarding library development
  • Added date picker




A case study on viable techniques for vanilla web development.