Tram-Deco

Declarative Custom Elements using native Web Component APIs and specs.

Tram-Deco provides a more elegant interface for building Web Components, that remains as close as possible to the existing browser APIs. Tram-Deco is an experiment to determine the value of a declarative interface for building Web Components, without the addition of APIs that don't already exist.

Example

<!-- include the Tram-Deco library -->
<script src="https://unpkg.com/tram-deco@6"></script>

<!-- define some web components -->
<template id="componentDefinitions">
  <!-- definition for a custom-title tag! -->
  <custom-title>
    <!-- declarative shadow dom for the insides -->
    <template shadowrootmode="open">
      <!-- styles, for just this element -->
      <style>
        h1 {
          color: blue;
        }
      </style>

      <!-- dom, to show on the page -->
      <h1>
        <slot>Hello World</slot>
      </h1>
      <hr />
    </template>

    <!-- scripts, that let you define lifecycle methods -->
    <script td-method="connectedCallback">
      this.shadowRoot.querySelector('slot').addEventListener('slotchange', () => {
        document.title = this.textContent || 'Hello World';
      });
    </script>
  </custom-title>
</template>

<!-- process the template to generate new definitions -->
<script>
  TramDeco.processTemplate(componentDefinitions);
</script>

<!-- use our new element! -->
<custom-title>Tram-Deco is Cool!</custom-title>

Live on Codepen

How to use

There are two ways to use Tram-Deco in your project - you can either have component definitions in your served HTML template (in template tags), or you can export the components as part of a build step to be imported with script tags.

Template Component Definitions

If you don't want a build step, or are just building components for a dedicated static page, you can do the following to write component definitions in your main template:

Include the Tram-Deco library (you can point to either tram-deco.js or tram-deco.min.js)

<script src="https://unpkg.com/tram-deco@6/tram-deco.min.js"></script>

Create a template tag with your component definitions, and then use Tram-Deco to process that template

<template id="myDefinitions">
  <!-- component definitions -->
</template>

<script>
  TramDeco.processTemplate(myDefinitions);
</script>

Export JS Definition

Important

Tram-Deco import depends on setHTMLUnsafe, which is a recently released feature. Check caniuse.com to understand browser support and coverage here.

If you want to export your component definition, to be used in other projects, or to organize the components in different files, you can do the following:

Create a component definition file (.html) - this can include as many top-level component definitions as you'd like.

<!-- my-counter.html -->
<my-counter>
  <template shadowrootmode="open">
    <!-- ... -->
  </template>
</my-counter>

Run the following command in the command line, or as part of a build step:

npx tram-deco export-components my-counter.html

This will create a JS file that can be imported using a standard script tag:

<script src="./my-counter.js">

API

JS API

TramDeco.processTemplate(templateTag)

The processTemplate function takes in a single template tag with several component definitions, and builds Web Component definitions for all of them in the global custom elements registry.

TramDeco.define(elementDefinition)

The define function takes in a single element definition and builds a Web Component definition for the global custom elements registry. It is the underlying method used in processTemplate, and probably does not need to be called in isolation.

Component API

These attributes can be used to provide or inherit logic for different life cycle events of your component. They follow the standard API for Web Components.

td-extends="tag-name"

Attribute to be used on the top-level definition tag. The class associated with the tag-name will be used as a parent class when building this Web Component definition. That tag must be already registered in the customElements registry.

td-property="propertyName"

Attribute to be used on a script tag in your component definition. The assigned property name will be attached to the element as a static property, and can be useful for adding observedAttributes, formAssociated, disableInternals, or disableShadow. You can also define custom static properties for your element.

td-method="methodName"

Attribute to be used on a script tag in your component definition. The assigned method name will be attached to the element, and can be useful for adding to the constructor, or setting other Web Component APIs, such as connectedCallback, disconnectedCallback, adoptedCallback, or attributeChangedCallback. You can also define custom methods for your element.

Tip

If you are using attributeChangedCallback you can access the parameters (name, oldValue, and newValue) using the arguments keyword. See the example below to see how this works!

Example Using Component API

<script src="https://unpkg.com/tram-deco@6"></script>

<template id="myCounter">
  <my-counter>
    <!-- observed attributes, to watch for attribute changes on count -->
    <script td-property="observedAttributes">
      ['count'];
    </script>

    <template shadowrootmode="open" shadowrootdelegatesfocus>
      <button><slot>Counter</slot>: <span>0</span></button>
    </template>

    <!-- when we mount this component, add an event listener -->
    <script td-method="connectedCallback">
      const button = this.shadowRoot.querySelector('button');
      button.addEventListener('click', (event) => {
        const newCount = parseInt(this.getAttribute('count')) + 1;
        this.setAttribute('count', newCount);
      });
    </script>

    <!-- when the count updates, update the template -->
    <script td-method="attributeChangedCallback">
      const [name, oldValue, newValue] = arguments;
      if (name === 'count') {
        const span = this.shadowRoot.querySelector('span');
        span.textContent = newValue;
      }
    </script>
  </my-counter>
</template>

<script>
  TramDeco.processTemplate(myCounter);
</script>

<my-counter count="0">Tram-Deco</my-counter>

Live on Codepen

contributions / discussions

If you think this is useful or interesting, I'd love to hear your thoughts! Feel free to reach out to me on mastodon, or join the Tram-One discord.