Temples: Declarative HTML Templates

This project is a rewriting of the original Temples template system based on jQuery. The new iteration replaces jQuery with a standard, DOM-based templating engine.

Synopsis

Temples (templates that you won't hate) is a templating system for HTML. Temples syntax is very easy to use and can be learned in 5 minutes. Temples is a declarative, DOM-based rendering engine, with a special ability for real-time and partial updates. Templates are plain HTML blocks or fragments decorated with a few data-bind attributes. Temples works in the browser and on the server, with the same engine and the same templates everywhere.

Motivations

I want a template system that :

is easy to use, easy to read, and predictable in its syntax.
won't break my pages with ugly non-HTML syntax that my IDE does not recognize.
is reliable, so that web designers can work on the markup and the CSS with very little chance of breaking the bindings.
can support real-time live updates of only the relevant data, without rendering the whole thing.
works seamlessly with structured data at any level of nesting.
is built on web platform standards, so that components stay reusable without a framework.

I want to :

use genuine HTML pages, full of example text, and transform them with the addition of a few data-bind attributes.
understand how it works in 2 minutes.
render the same templates in the browser and on the server, for fast and SEO-friendly pages.

Features

Fully HTML5 compliant. Won't break your pages.
Declarative bindings with a predictable syntax.
Transparent rendering of structured data, with functions as computed values.
Real-time partial updates of only the bound values.
Standalone engine, free of any framework dependency.
Web Components made declarative through the TemplesComponent base class.
Server-side rendering (SSR) and static site generation (SSG) with linkedom, on Bun, Node.js, or Deno.
Optional jQuery plugin for jQuery-based pages.

The engine in three forms

The standalone Renderer class for direct use in the browser and for server-side rendering (SSR) in Bun, Node.js, or Deno.
The TemplesComponent base class for declarative Web Components.
A jQuery plugin (temples/jquery) that renders data into matched elements.

DATA BINDING SYNTAX

The syntax stays the same, only relying on a few specific data attributes : data-bind (inline values), data-iterate (loop), data-render-if (condition).

All binding paths are resolved against the component's internal this.data object (see Attributes: the single source of truth).

`data-bind` — inline values

Expressions are of the form : [value|text|html|<attr-name>]=<path.to.data> Multiple updates can be specified, separated by a comma ','.

Here is for example the block of markup you'd wish to use to display the currently logged user :

<div id="logged-user">
    <img data-bind="src=user.avatar, title=user.fullname" title="John DOE" src="http://avatar.com/johndoe" />
    <div data-bind="user.fullname, class=user.status" class="active">John DOE</div>
</div>

Notice how we don't have to get rid of the sample text, so that the markup still displays nicely in the browser before the data is bound.

Depending on the context, value= or html= can be omitted so that :

<div data-bind="html=user.fullname">John DOE</div>

is equivalent to :

<div data-bind="user.fullname">John DOE</div>

and

<input type="text" data-bind="value=user.name" />

is equivalent to :

<input type="text" data-bind="user.name" />

Binding the `class` attribute

There is a special syntax for the class attribute allowing you to specify the values you want to toggle. Because the class attribute is a space-separated list of values, you usually want to toggle certain values within a particular range, leaving the others untouched. This is exactly what you can do with the extended data-bind syntax for the class attribute :

<div class="row container" data-bind="class[article|quote|tweet]=article.type" />

In this example, the binding value of article.type will be evaluated, and used to replace one of these values within the class attribute : article, quote or tweet. All other class values (ie : row and container in our example) will be left untouched.

`data-iterate` — loops

Temples can iterate over collections to build a list of items. This is done with the data-iterate attribute that designates the collection to iterate on, optionally names the variable to hold the iteration value, and uses the first-level sub-template to render the child elements.

If no variable name is provided, Temples will automatically choose one by suppressing the final s on the collection's name.

<!-- Introducing a list of quotes -->
<div data-iterate="quote: article.quotes">
    <div class="quote" data-bind="quote">I ain't a native : I was born there!</div>
</div>

<!-- Will automatically iterate on the 'tag' variable -->
<ul data-iterate="article.tags">
    <li><a data-bind="tag.label, href=tag.url">peace</a></li>
</ul>

Alternate syntax

This attribute offers several syntactical variants to suit your expressive needs :

data-each can be used in place of data-iterate.
The variable name can be introduced with : or with the from keyword.

So that each of these iterative blocks have the same meaning :

<div data-iterate="article.quotes">...</div>

<div data-iterate="quote: article.quotes">...</div>

<div data-iterate="quote from article.quotes">...</div>

<div data-each="quote from article.quotes">...</div>

`data-render-if` — conditionals

Another useful feature is the possibility to associate the rendering of a block element to a condition. This is done with the data-render-if attribute, whose value must evaluate to a boolean condition.

<!-- Display a special icon if this article is 'featured' -->
<div class="icon" data-render-if="article.featured">
  <img src="featured.png" />
</div>

<!-- Display another icon if this article is 'popular' -->
<div class="icon" data-render-if="article.popular">
    <img src="popular.png" />
</div>

The test can be done against a function in the data if needed :

{
    article: {
        featured: true,
        popular: function() {
            return (this.comments.length > 20);
        }
    }
}

STANDALONE TEMPLATE ENGINE

The binding engine is a standalone module. It does not depend on the Web Component lifecycle. Build a renderer with the Renderer class.

The v0 name-based Temples registry (prepare(), render(name, ...), update(name, ...), renderToString(name, ...), destroy(name)) is deprecated. It stored Renderer instances by name, and a forgotten destroy(name) left zombie templates. Direct Renderer instances are owned by the caller, so no registry and no destroy() are needed.

The `Renderer` class

The template source can be :

an HTML string with the full template content.
a DOM element.

const renderer = new Renderer(document.getElementById("logged-user")); // DOM element
const renderer = new Renderer('<div><span data-bind="user.firstname">John</span></div>'); // HTML string

`render(data)`

Renders the template with the data and returns the updated template DOM. render touches only the paths present in data; absent paths keep their current state. Pass a full dictionary to render everything, or a partial dictionary to re-render only the paths it carries. The returned DOM lets you insert, clone, or serialize the result.

const renderer = new Renderer(document.getElementById("logged-user"));
const result = renderer.render(user);
document.body.appendChild(result);

To update a single path in real time, use update instead (see below).

`update(propertyPath, value)`

Updates a single path and re-renders only the binding for that exact path. The path is a dotted path such as "user.status". This enables efficient real-time partial updates without re-rendering the whole template.

// Real-time partial update of one path only
renderer.update("user.status", "away");

`toHtml()` / `renderToString()`

Returns the serialized HTML of the rendered template. renderToString() is a synonym for toHtml(). This method is the entry point for server-side rendering (SSR) and static site generation (SSG).

import { Renderer } from "temples";
import "temples/ssr";

const renderer = new Renderer(articleTemplateMarkup);
renderer.render({
  article: {
    title: "The Great Race",
    quotes: ["Quiet!", "Pardon me Mr Partner."]
  }
});

const html = renderer.renderToString();

// Write the HTML string to a file with your runtime file API (Bun, Node.js, Deno).

Server-side rendering

The engine operates on a DOM. In the browser it uses the native document. On the server there is no DOM, so the engine uses linkedom to parse and serialize the HTML.

Import the SSR entry to use the engine on the server :

import "temples/ssr";

The temples/ssr entry wires the engine to linkedom. The main entry never imports linkedom, so browser bundles stay small.

WEB COMPONENT IMPLEMENTATION

1. Declaration

The Web Component implementation is contained in our exported class TemplesComponent. Instead of inheriting from HTMLElement to create a new Web component, you inherit from TemplesComponent :

import { TemplesComponent } from "./Temples";

/**
 * Classical Web component class definition
 */
export class MyComponent extends HTMLElement {
}

/**
 * Use TemplesComponent to inherit the full declarative templating system
 */
export class MyTemplesComponent extends TemplesComponent {
}

2. Component structure (html template, script, style)

Each aspect of the component : the markup (with the data-* binding attributes), the style and the event handling for dynamic components with state MUST be written in separate source files with their according type, and an index.ts file binds all these sources together to export the TemplesComponent :

<component>.html — the component's markup template with data-* binding attributes
<component>.[ts|js] — the component's event handlers (exported as an event map)
<component>.css — the component's styles, scoped by the component's tag name
index.ts — assembles all parts, defines the component class, and registers the custom element

A user could inline all parts in a single file, but we propose this clean approach where each concern is separated into its own file. This lets designers work on markup and CSS freely, with very little chance of breaking the binding logic.

3. Assembly in `index.ts`

The index.ts file is where all the parts come together. It imports the template, styles, and event handlers, defines the component class, and registers the custom element with TemplesComponent.define() :

import { TemplesComponent } from "../Temples";
import template from "./flipping-card.html";
import "./flipping-card.css";
import { events } from "./flipping-card.js";

export class FlippingCard extends TemplesComponent {
  static observedAttributes = ["title", "flipped"];

  // Semantic state-transition methods (public API)
  flip() { this.setAttribute("flipped", "true"); }
  unflip() { this.setAttribute("flipped", "false"); }
}

// Register the custom element with its template and events
TemplesComponent.define("flipping-card", FlippingCard, { template, events });

Bun natively supports importing .html files as strings and .css files (which are injected into the page). No additional build step is required.

4. The `<template>` mechanism

When TemplesComponent.define() is called, the template HTML string is parsed once into a <template> element and stored on the class. Each time a component instance connects to the DOM (connectedCallback), the template content is cloned via template.content.cloneNode(true) and appended as the component's children.

This is the cleanest and most efficient approach — the HTML is parsed a single time, and each instance receives a fast DOM clone rather than a re-parse or an innerHTML assignment.

5. Attributes: the single source of truth

A component's data is derived from its plain HTML attributes (no data- prefix — that prefix is reserved for internal template bindings). The component declares which attributes it observes via the standard static observedAttributes array :

static observedAttributes = ["title", "flipped"];

When any observed attribute changes (including the initial values present in the markup), attributeChangedCallback fires, the attribute's value is aggregated into the internal this.data object, and a re-render is triggered automatically.

<!-- Attributes are the idiomatic way to configure a component -->
<flipping-card title="Hello World" flipped="false"></flipping-card>

// Mutating an attribute triggers a re-render
card.setAttribute("flipped", "true");

this.data is private — it cannot be directly modified from outside. It may contain additional internal state properties that are not exposed as attributes (enriched by the component's own logic), but the attributes are the authoritative source that dictates the component's state.

6. State and reactivity

The internal rendering pipeline :

this.data (private) — the aggregated state object, built from observed attributes and optionally enriched by internal logic.
render() (internal) — re-renders all data-bind / data-iterate / data-render-if bindings from the current this.data.
update(propertyPath, value) (internal) — patches a single path in this.data (e.g. "article.title") and re-renders only the affected binding. This enables efficient partial updates, ideal for real-time pushed notifications.

These methods are internal to the component. External code must not call render(data) to arbitrarily overwrite component state. The current attribute values are the source of truth that dictates the component state. The same binding engine is public through the Renderer class (see Standalone template engine).

To change a component's state, use either :

Mutate attributes (idiomatic) — element.setAttribute("flipped", "true")
Call semantic state-transition methods (state machine pattern) — element.flip()

State-transition methods are public methods defined by the component author that internally change attributes or call update() :

flip() { this.setAttribute("flipped", "true"); }

7. Event handling with `registerEvents()`

The .js (or .ts) file exports an event map — a declarative mapping of "<eventType> <selector>": handler entries. Each handler receives the component instance (host) as its argument, giving it privileged internal access to update() and render() :

// flipping-card.js
export const events = {
  "click .flip-btn": (host) => host.flip(),
  "click .back-btn": (host) => host.unflip()
};

The event map is passed to TemplesComponent.define() and registered automatically during connectedCallback via the registerEvents() helper. Event listeners are cleaned up in disconnectedCallback to prevent memory leaks.

Though event handlers have access to host.update() and host.render(), the preferred pattern is to go through attributes or semantic state-transition methods — keeping attributes as the single source of truth.

8. Styling

Styles live in the component's .css file and are imported via Bun's CSS import (import "./component.css"). Since we use Light DOM (no Shadow DOM), all CSS rules must be scoped by the component's tag name to avoid clashes with the page's global styles :

/* flipping-card.css */
flipping-card {
  display: inline-block;
  perspective: 1000px;
}

flipping-card .card-inner {
  transition: transform 0.6s;
  transform-style: preserve-3d;
}

flipping-card[flipped="true"] .card-inner {
  transform: rotateY(180deg);
}

This approach allows the component to inherit and use all global theming variables available on the page, while preventing style collisions through tag-name scoping.

Shadow DOM support may be added in a future version for use cases that require full style encapsulation.

TemplesComponent API Reference

Static methods

`TemplesComponent.define(tagName, ComponentClass, options)`

Registers a custom element and associates it with its template and events. Parses the template HTML string into a <template> element (once) and calls customElements.define().

Parameter	Type	Description
`tagName`	`string`	The custom element tag name (must contain a hyphen)
`ComponentClass`	`typeof TemplesComponent`	The class extending `TemplesComponent`
`options.template`	`string`	The HTML template string (imported from the `.html` file)
`options.events`	`EventMap`	Optional event handler map (imported from the `.js` file)

TemplesComponent.define("flipping-card", FlippingCard, { template, events });

Static properties (overridden by subclasses)

`static observedAttributes: string[]`

Standard Web Component property. Lists the plain attribute names that the component observes. When any of these attributes change, the value is aggregated into this.data and a re-render is triggered.

static observedAttributes = ["title", "flipped"];

Instance properties

`this.data` (private)

The internal state object. Built from observed attributes on connection, and optionally enriched by the component's internal logic via update(). Not directly accessible or modifiable from outside the component.

Internal methods

`render()`

Re-renders all data-bind, data-iterate, and data-render-if bindings from the current this.data. Called automatically when attributes change. Accessible from event handlers and internal component logic, but internal to the component. Delegates to the shared Renderer engine (see Standalone template engine).

`update(propertyPath, value)`

Patches a single path in this.data (e.g. "article.title") and re-renders only the affected binding. Enables efficient partial updates without re-rendering the entire component. Accessible from event handlers and internal component logic, but internal to the component. Delegates to the shared engine's update() method.

Public methods (user-defined)

State-transition methods defined by the component author. These are the idiomatic way to change a component's state programmatically — they encapsulate state changes behind a meaningful API rather than exposing raw attribute manipulation :

flip() { this.setAttribute("flipped", "true"); }
unflip() { this.setAttribute("flipped", "false"); }

Lifecycle hooks

TemplesComponent implements the standard Web Component lifecycle :

Hook	Behavior
`connectedCallback`	Clones the template content into the component, registers event listeners, performs initial render from current attribute values
`disconnectedCallback`	Removes event listeners and frees bound resources
`attributeChangedCallback`	Aggregates the changed attribute into `this.data` and triggers a re-render

Helper: `registerEvents(host, eventMap)`

Registers event listeners on the component instance. Called internally by the base class during connectedCallback.

Parameter	Type	Description
`host`	`TemplesComponent`	The component instance
`eventMap`	`Record<string, (host) => void>`	Map of `"<eventType> <selector>": handler` entries

const events = {
  "click .flip-btn": (host) => host.flip()
};
registerEvents(host, events);

JQUERY PLUGIN

A separate, tree-shakeable export provides the jQuery-compatible version of the engine. Import the temples/jquery entry to register the plugin :

import "temples/jquery";

The plugin adds the $.fn.temples method :

$(".list").temples(data); // render data into each matched element
const renderer = $(".list").temples(); // get the prepared Renderer

jQuery is a peer dependency of this export. The main entry never touches $.

Complete example: flipping-card

A simple flip card component demonstrating all the pieces working together.

flipping-card.html — the template :

<div class="card-inner">
  <div class="card-front">
    <h2 data-bind="title">Card Title</h2>
    <button class="flip-btn">Flip</button>
  </div>
  <div class="card-back">
    <button class="back-btn">Back</button>
  </div>
</div>

flipping-card.js — the event handlers :

export const events = {
  "click .flip-btn": (host) => host.flip(),
  "click .back-btn": (host) => host.unflip()
};

flipping-card.css — the styles (scoped by tag name) :

flipping-card {
  display: inline-block;
  perspective: 1000px;
  width: 200px;
  height: 300px;
}

flipping-card .card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.6s;
  transform-style: preserve-3d;
}

flipping-card[flipped="true"] .card-inner {
  transform: rotateY(180deg);
}

flipping-card .card-front,
flipping-card .card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
}

flipping-card .card-back {
  transform: rotateY(180deg);
}

index.ts — assembly and registration :

import { TemplesComponent } from "../Temples";
import template from "./flipping-card.html";
import "./flipping-card.css";
import { events } from "./flipping-card.js";

export class FlippingCard extends TemplesComponent {
  static observedAttributes = ["title", "flipped"];

  flip() { this.setAttribute("flipped", "true"); }
  unflip() { this.setAttribute("flipped", "false"); }
}

TemplesComponent.define("flipping-card", FlippingCard, { template, events });

Usage in a page :

<!DOCTYPE html>
<html>
<body>
  <flipping-card title="Hello World" flipped="false"></flipping-card>
  <script type="module" src="./example/components/flipping-card/index.ts"></script>
</body>
</html>

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README.md		README.md
biome.jsonc		biome.jsonc
bun.lock		bun.lock
bunfig.toml		bunfig.toml
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tsconfig.json		tsconfig.json

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Temples: Declarative HTML Templates

Synopsis

Motivations

Features

The engine in three forms

DATA BINDING SYNTAX

data-bind — inline values

Binding the class attribute

data-iterate — loops

Alternate syntax

data-render-if — conditionals

STANDALONE TEMPLATE ENGINE

The Renderer class

render(data)

update(propertyPath, value)

toHtml() / renderToString()

Server-side rendering

WEB COMPONENT IMPLEMENTATION

1. Declaration

2. Component structure (html template, script, style)

3. Assembly in index.ts

4. The <template> mechanism

5. Attributes: the single source of truth

6. State and reactivity

7. Event handling with registerEvents()

8. Styling

TemplesComponent API Reference

Static methods

TemplesComponent.define(tagName, ComponentClass, options)

Static properties (overridden by subclasses)

static observedAttributes: string[]

Instance properties

this.data (private)

Internal methods

render()

update(propertyPath, value)

Public methods (user-defined)

Lifecycle hooks

Helper: registerEvents(host, eventMap)

JQUERY PLUGIN

Complete example: flipping-card

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`data-bind` — inline values

Binding the `class` attribute

`data-iterate` — loops

`data-render-if` — conditionals

The `Renderer` class

`render(data)`

`update(propertyPath, value)`

`toHtml()` / `renderToString()`

3. Assembly in `index.ts`

4. The `<template>` mechanism

7. Event handling with `registerEvents()`

`TemplesComponent.define(tagName, ComponentClass, options)`

`static observedAttributes: string[]`

`this.data` (private)

`render()`

`update(propertyPath, value)`

Helper: `registerEvents(host, eventMap)`