a rollup plugin for encoding html files as javascript modules
Last updated 4 months ago by odedshr .
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$ cnpm install rollup-plugin-html-encoder 
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Rollup Plugin HTML Encoder


This Rollup plugin lets you import HTML files and use them as classes in your javascript code.


npm install --save-dev rollup-plugin-html-encoder


Add the html-encoder to the rollup.config.js:

import { rollup } from 'rollup';
import html from 'rollup-plugin-html-encoder';

	entry: 'main.js',
	plugins: [
			include: '**/*.html'

You may import HTML files in your javascript code this way:

import Node from './popup.template.html'

document.body.append(new Node());

Usage in Node.JS

The properly create a DOM node you'll need a DOMParser, which exists in the browser but not in Node.JS. You can obtain it from the XMLDOM dependency:

import Node from './page.template.html'
import { DOMParser } from 'xmldom';

Node.DOMParser = DOMParser;

return (new Node()).toString();

Dynamic Content

HTML-encoder supports dynamic content using XML-processing-instructions and passing an object of data to the constructor (e.g. new Node({data})). These instructions are applied to their preceeding sibling tag or parent if no preceeding tag availble. For example for the data

<div><?css parent?><b>Hello</b><?css sibling?></div>`

import Node from './template.html';
console.log((new Node({ parent: 'parent', sibling: 'sibling'})).toString) 
// ouptput: <div class="parent"><b class="sibling">Hello</b></div>


  1. <?=text?> will append a textNode with the html-safe content of the variable text.
  2. <?==html?> will append a parsed node with the content of the variable html. The input may be either a text or a pre-compiled node.


  1. <??condition>xxx<?/??> will add its content only if the variable condition is truthy.
  2. <??!condition>xxx<?/??> will add its content only if the variable condition is falsy.


  1. <?value@array?><li><?=value?></li></?@?> will iterate over an array allowing access to its elements.
  2. <?value:key@array?><li><?=key?> <?=value?></li></?@?>_ will iterate over an array allowing access to its elements and provide their index-number (starting from zero)
  3. <?value:key@object?><li><?=key?> <?=value?></li></?@?> will iterate over a key-value object.


  1. <?attr key=value?> will set the attribute key with the value of value.
  2. <?attr key=value key2=value2?> will set as many attributes as provided.
  3. <?attr map?> will set a collection of attributes described in the variable map
  4. <?attr condition?key=value?> will set attribute key only if the variable condition is truthy.
  5. <?attr !condition?key=value?> will set attribute key only if the variable condition is falsy.
  6. <?attr condition?map?> will set a collection of attributes only if the variable condition is truthy.
  7. <?attr !condition?map?> will set a collection of attributes only if the variable condition is falsy.

CSS Classes

  1. <?css value?> will add the css-class or array-of-classes provided in value.
  2. <?css condition?value?> will add the css-class or array-of-classes provided in value if the variable condition is truthy.

Easy-access to Content

HTML elements with an id attribute can easily be acceses at node.set[id], for example:

<button id="cta">Foo</div>

const node = new Node();
node.set.cta.addEventListener('click', ... );

text nodes and html nodes that were added using <?=text ?> and <?==html ?> can also have quick-access, by adding a #id suffix. For example:

<div>Hello <?=firstName #name?></div>

const node = new Node({ firstName: 'Adam' });
console.log(node.toString()); // output `<div>Hello Adam</div>` = 'Ben';
console.log(node.toString()); // output `<div>Hello Ben</div>`
  1. <?=text #id?> => create a textnode and update its value
  2. <?==html #id?> => create a node and update its value with either text or node


it is possible to use existing templates using the <?:templateNamte?> command. For example:

liTemplate: <li><?=v?></li>
ulTemplate: <ul><?v@items?><?:liTemplate?><?/@?></ul>'

console.log(new UlTemplate({ items: ['a','b','c'], liTemplate }).toString())
// output: <ul><li>a</li><li>b</li><li>c</li></ul>

The idea behind the project

The HTML <template> element can be useful when (a) we have repetitive HTML content; or (b) when we're introducing new content. But because of the static nature of HTML which doesn't really support any data-binding on its own, the template element becomes meaningless. I believe that there is a conceptual flaw with HTML <template> element (or at least it is I who failed to find a reasonable tutorial how to use it properly): <template> tags are meant to help having dynamic content in the page by providing the template as base, but as long as it is handled using javascript and not a pure-browser-native code, it must be encoded (for performance sake) to javascript before being used, and if the translation occurs at the browser-side then by definition it'll effect performance.

How could it have worked natively?

  1. <template> tag should have a data-bind attribute, which is then connected to a javascript variable hold an object (or array of objects) with fields that will be populated natively. For example - <template data-bind="names"><li data-bind="name"><li></template> would be displayed as <li>Alex</li><li>Ben</li> And wouldn't it be wonderful if whenever names variable would update the html would refresh itself automatically?
  2. If we could data-bind-src a URL with either JSON or XML data to be natively parsed into our template. But in all fairness, we don't need a template tag for that, we just need the html bind attribute. This would work great for pseudo-static HTML files (in the sense that there's no Javascript required for the page to function), and should we want a dynamic page perhaps we could pick the TemplateElement and use it's clone(data) method to populate it with our data, so the usage would be:
const template = document.selectById("myTemplate");
document.selectById("myParent").appendChild(template.clone(data, isWatchingData)

Without native-browser-based data-population and without javascript-less support, the template tags are utter pointless.

JSX as a templating alternative

And now let's talk about JSX, which is another kind of template. JSX in essence, is a pseudo-html code written within JS code and then pre-compiled to pure JS which is served to the browser. It's a much more efficient way to write template but I don't like it, because in order to write proper JSX you need to proficient in both HTML and Javascript and for me it feels like a mix of responsibilities. HTML provides the structure to our page, while javascript provides computability and these are two different things from my point of view.

This is where the html-encoder comes in

I would like to write a normal HTML file but empower it with a data-bind attribute without any additional javascript programming (it would have been nice to do so natively but that's just wishful thinking) and this HTML can be pre-compiled on the server and served as a static page (live-refresh is bonus). The HTML encoder does exactly that:

  1. Write a normal HTML file
  2. Import it to your javascript code using import Node from./example.template.html;and then use it by appending it to the DOM -document.appendChild(new Node());`

Behind the scenes, I use Rollup plugin capability to detect imported HTML and encoding them to a set of javascript commands that are embedded with the Rollup output javascript file.

Adding dynamic content

A guiding principle was to write an HTML valid code, but this raised the question - "Where can we place the computational instructions required?" and I found the Process Instructions (PI for short). they look a bit ugly I must admit - <?=value?> but for the proof-of-concept they serve their purpose. Looking at other templating systems such as Vue, the PIs are attributes in the elements or new html-invalid elements (i.e. not part of the HTML language). The <? ... ?> is a valid HTML element, it should appear as a first child to the element we wish to manipulate or immediately following it (in case of a childless element).


  1. <?=text?> creates a textNode with the content of the variable named text.
  2. <?==html?> creates an HTML element with the content of html, which can be either an HTML element or a string that will be parsed as HTML.
  3. Conditions: <??condition?>xxx<?/??> will add the content only if condition is true. A boolean-negate (!) is also available so <??!condition?>xxx<?/??> will add the content only if condition is false.
  4. Loops: <?item:index@items?>xxx<?/@?> will iterate over items (either an array or an object) providing the key and value and the given variable names (in the example it would be item and index)
  5. Attributes: <?attr key1=varName1 key2=varName2?> will set the attributes in preceding element <?attr attrObject?> will set the attributes described in the attrObject (i.e. the key is the attribute name and the value is the actual value)
  6. CSS classes: <?css varName?> will set the class(es) described in the variable that can be either a string or an array. it's also possible to condition a class by writing <?class condition?varName?>.
  7. Editable content: you can access created nodes at if the id was provided in one of those ways <?=text #foo?> or <?==html #foo?> or <div id="foo">.
  8. SubTemplates: When a subTemplates' class is provided with the data it can be used with <?:subTemplateVarName?> and it will get the data as the parent-template.

Future steps

This project is mostly thought-experiment in creating a relatively clean internet code, well-encapsulated and easy to use. The next step will be to try create an application with it and see whether it holds to its promise and allows easy development with no need to touch HTML code directly from the javascript.

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