ThymeleafJS

A basic implementation of the Thymeleaf templating engine in JavaScript.

Having worked with Thymeleaf for several years, other templating languages are starting to look foreign to me. Upon evaluating several existing JavaScript templating languages to help build a mock Node server for development, it made me yearn for the natural templating feature of Thymeleaf.

This project aims first to perform similar tasks to existing JS templating libraries like Mustache on Node servers like Express. Once the Thymeleaf-in-JS dream is achieved, I can start thinking about stretch goals to make it a better companion to the original Thymeleaf for web development :)

Current goals

This project already works very well as a server-side template renderer, but now I'm trying to get it to play nice with the original Thymeleaf, ie: render templates on the server with Thymeleaf, then re-render the templates on the client using ThymeleafJS with the same template code (I've been calling this feature "isomorphic templating", akin to isomorphic JavaScript where the same code is run on the client and server).

To help with this, I've written a simple TODO app in Spring Boot w/ Thymeleaf and am using ThymeleafJS to test and develop this feature. The TODO app can be found here: https://github.com/ultraq/thymeleafjs-todo

Natural Templates

For those unfamiliar with Thymeleaf, it's main feature is being able to use natural templates - HTML that can be correctly displayed in browsers and also work as static prototypes, allowing for stronger collaboration in development teams.

Borrowing the example from the front page of the Thymeleaf website:

<p>Hello <span thjs:text="${username}">(username)</span>
You're using Thymeleaf for JavaScript!  Wanna see some random fruit?</p>
<ul>
  <li thjs:each="product: ${allProducts}">
    <div thjs:text="${product.name}">Oranges</div>
    <div thjs:text="${product.price}">0.99</div>
  </li>
</ul>

Installation

Via NPM:

npm install thymeleaf --save

API

thymeleafjs is still under development, denoted by the 0.x semver, so expect anything below to change.

Create a new instance of a Thymeleaf TemplateEngine, then use one of its process* functions to process your Thymeleaf template, eg:

import {TemplateEngine} from 'thymeleaf';

let templateEngine = new TemplateEngine();

// Render template from string
templateEngine.process('<div thjs:text="${greeting}">(greeting)</div>', { greeting: 'Hello!' })
  .then(result => {
    // Do something with the result...
  });

// Render template from file
templateEngine.processFile('template.html', { greeting: 'Hello!' })
  .then(result => {
    // Do something with the result...
  });

TemplateEngine

The main class for the processing of templates.

new TemplateEngine(options)

When constructing a new instance of the template engine, a config object can be passed in to set any of the available options. These are:

• dialects: array of Dialect instances to use in processing
• messageResolver: a function given a message key and optional message parameters which should then return the message string or Promise of the message string. Required if you want to use message expressions (#{...}).
• templateResolver: a function supplied the template name which should then return the text or a Promise that will resolve with the text of the template being requested. Required if you want to make use of template fragment processors like th:insert.

import {StandardDialect, TemplateEngine} from 'thymeleaf';

let templateEngine = new TemplateEngine({
  dialects: [
    new StandardDialect('th', { // Enable isomorphic mode with this config object
      prefix: 'thjs'
    })
  ],
  messageResolver: (key, parameters) => {
  	// ...
  },
  templateResolver: templateName => {
  	// ...
  }
});

process(templateString, context)

Process the Thymeleaf template, returning a Promise which is resolved with the processed template.

• template: a Thymeleaf template string to process
• context: an object of key/value pairs, what the expressions evaluate to and the values they're set to

processFile(templateFile, context)

Process the Thymeleaf template at the given file location, returning a Promise which is resolved with the processed template.

• templateFile: path to the Thymeleaf template to process
• context: an object of key/value pairs, what the expressions evaluate to and the values they're set to

Dialect

A basic class that is used as a template for implementing dialects that contain processors and expression objects to expand Thymeleaf's functionality. The Standard Dialect is itself an instance of Dialect.

To add processors, create a class that extends Dialect, and add either a processors property or getter which is an array of processors.

To add expression objects, extend Dialect and add either a expressionObjects property or getter which is an object whose keys are the expression object names (starting with # as the convention from Thymeleaf) and the values are the expression objects.

AttributeProcessor

A basic class that is used for creating processors that work using HTML attributes.

ElementProcessor

A processor for working on HTML elements.

StandardDialect

The built-in dialect that provides all the functionality that Thymeleaf is known for. Importing this class is only useful for specifying a prefix different from the default of thjs, eg:

import {TemplateEngine, StandardDialect} from 'thymeleaf';

let templateEngine = new TemplateEngine({
  dialects: [
    new StandardDialect('th')
  ]
});

Use the STANDARD_CONFIGURATION export to do this more succinctly.

STANDARD_CONFIGURATION

A configuration object used to set the prefix to the th that many of us will be used to from the original Thymeleaf. It also enables the experimental "isomorphic mode", in which ThymeleafJS can also process original Thymeleaf processing instructions, unless a thjs one is specified for the same name, in which case that will take precedence.

import {TemplateEngine, STANDARD_CONFIGURATION} from 'thymeleaf';

let templateEngine = new TemplateEngine(STANDARD_CONFIGURATION);

Supported features (so far)

See here for supported processors: https://github.com/ultraq/thymeleafjs/issues/21

See here for supported expression syntaxes: https://github.com/ultraq/thymeleafjs/issues/20

See here for supported expression objects: https://github.com/ultraq/thymeleafjs/issues/31

Integration

Express

Integration with the Express server is its own module, express-thymeleaf. Installation and usage instructions are also in that project's readme.