h t m l h a m m e r

JavaScript HTML template engine and a WebComponents library.

Features

• Write HTML with JavaScript using real HTML tag names.
• Unique way of building WebComponents

Why?

• String literals tend to get messy and unreadable
• Maybe you don't want or need JSX
• HyperScript is ok, but you would like to avoid manually writing HTML tag names
• Make writing HTML in JavaScript feel almost like writing it in .html file
• Make writing HTML in JavaScript dead simple and intuitive but keeping all the JavaScript's power

Install

github

• Latest version: npm install git+https://github.com/vsmid/htmlhammer.git --save

• Specific version: npm install git+https://github.com/vsmid/htmlhammer.git\#1.0.0 --save

npmjs

npm i htmlhammer

unpkg

<!-- Latest version CJS -->
<script src="https://unpkg.com/htmlhammer"></script>

<!-- Version 1.0.1 CJS -->
<script src="https://unpkg.com/htmlhammer@1.0.1"></script>

<!-- Latest version ESM -->
<script type="module">
  import { div } from 'https://unpkg.com/htmlhammer?module';
</script>

<!-- Latest version single file IIFE -->
<script src="https://unpkg.com/htmlhammer/htmlhammer.js"></script>

<!-- Latest version minified single file IIFE -->
<script src="https://unpkg.com/htmlhammer/htmlhammer.min.js"></script>

For specific versions use url format: unpkg.com/:package@:version/:file. See UNPKG for more info.

Importing and using htmlhammer

// In html
<script src="./htmlhammer.js"></script>;
const { div } = htmlhammer;

// In modules
const { div, a, h1 } = require('htmlhammer').default;
import { div, a, h1 } from 'htmlhammer';

Using htmlhammer

Supported HTML tags/elements

See the list on MDN. Tags/elements marked as obsolete/deprecated are not supported.

Signature

// Function name htmltagname is one of supported HTML tag/elements, e.g. div, a, h1, table etc.
// Since version 2.3.0 attributesAndProperties parameter is optional
htmltagname((attributesAndProperties = {}), ...children);

Parameters:

• attributesAndProperties - JSON object where key is the name of the element's attribute/property (e.g. id, name, style, onclick, or custom attribute/property etc. ) and value is the new attribute/property value. Difference between defining an attribute and property is that property value must always be one of function, instance of class, array or json object. This rule does not apply to reserved element attributes/properties and style.
• children - element or elements to be appended to parent element. Can be string, number, another HTMLElement created regularly or by htmlhammer, function returning one of the previously stated types etc.

Returns:

• An array of HTMLElement or a single HTMLElement.

Code sample

let items = [{ value: 1 }, { value: 2 }];

document.body.append(
  div(
    { style: { color: 'red' } },
    h1('I am the title'),
    a({ href: '#' }, 'Click me!'),
    table(tr({ $for: items }, item => td(item.value)))
  )
);

String as HTML

If you have HTML in string format and you would like for it to be added to element as HTML you should wrap it in HtmlString class. This is useful when you want to inject an already generated HTML in string format to an element ( e.g. HTML content received from REST service).

import { div, HtmlString } from './esm/index.js';

const html = '<h1>Hello World!</h1>';

document.body.append(
  div(new HtmlString(html)) // Without HTMLString wrapper, html content would be treated as text content hence text node would be created
);

Version 2.1.0 introduced a new attribute handler $apply which allows you to create inline element in any way you like.

const RawHtml = data => el => (el.innerHTML = data);

document.body.append(
  div(span({ $apply: RawHtml('<h1>Hello World!</h1>') }))
);

For more complex and complete examples see demo.

Reserved element attributes/properties

$for - creating multiple elements of the same type

// Creates three elements of type div, <div>1</div>, <div>2</div>, <div>3</div>
// index parameter is optional
// item = 1, index = 0
// item = 2, index = 1
// item = 3, index = 2
div({ $for: [1, 2, 3] }, (item, index) => item);

$if - conditionally create element

div({ $if: true }, 'I am created');
div({ $if: () => true }, 'I am created');

// Create only items with value > 2
div({ $for: [1, 2, 3], $if: item => item > 2 }, item => item);

$ref - reference created element

A key under which element will be stored must be an object!

const { div, ref, setRef } = htmlhammer;

// Reference by object
let obj = {};

// Prior to 2.2.0
let element = div({ $ref: setRef(obj) }, 'Hello World!');

// Version 2.2.0 allows ref to be set just by passing an object reference
let element = div({ $ref: obj }, 'Hello World!');

console.log(ref(obj) === element);

// Manually assigning id if the same object is used for multiple references
let person = new Person('Lena', 0);

div({ $ref: setRef(person, 'name') }, person.name);
div({ $ref: setRef(person, 'age') }, person.age);

console.log(ref(person, 'name'));
console.log(ref(person, 'age'));

// If used in combination with $for do not set object reference manually because it will automatically be set to the list item value
element = div(
  { $for: [{ v: 1 }, { v: 2 }, { v: 3 }], $ref: setRef },
  'Hello World!'
);

$apply - apply anything to an element

Use this attribute to apply anything to an element. This gives you the full power of JavaScript Element API mixed within htmlhammer's inline element creation. This can also be ideal for sharing style, logic, event handlers etc. across multiple components/elements. $apply can be given as a function which receives element or an array of such functions.

const RedText = el => (el.style.color = 'red');

// Function which can replace new HtmlString("<h1>Hello</h1>")
const HTMLContent = data => el => (el.innerHTML = data);

// Valid usages
div({ $apply: RedText });
div({ $apply: [RedText, HTMLContent('<h1>Hello</h1>')] });

Setting on-event actions

Event names are case-sensitive. For each event use corresponding element's event name.

// Defines element's onclick event function
a({ onclick: e => alert('Clicked!') }, 'Click me');
// Defines plain function on element, will not trigger on click
a({ onClick: e => alert('Clicked!') }, 'Click me');

Setting CSS

CSS is given in the form of JSON object when using element's style attribute or HTMLStyleElement when using HTML tag style.

// Global, using HTMLStyleElement
document.head.append(
  style(`
      body {
        font-size: 12px;
      }`)
);

// Inline, using style attribute
div(
  { style: { color: 'red', fontSize: '12px' } },
  'Hello World!'
);

When setting style attribute values, use corresponding JavaScript CSS property names. See MDN.

Custom child appender

Version 2.0.0 introduced option to provide a custom way of how child element is appended to parent element. Use case for this can be seen in HtmlString appender where raw html in the form of string needs to inserted to DOM element. For this to happen, element's insertAdjacentHTML method is used instead of default append method. See how HtmlString appender is implemented in appenders.js.

DocumentFragment

htmlhammer provides support for creating DocumentFragment object by simply using fragment function just like any other html tag function already provided. Even though it is not a true html tag it is here as a convenience function.

See how it relates to fragment used by JSX

import { fragment, div } from './esm/index.js';

fragment(div('1'), div('2'));

Custom elements

Method signature

customElement(tagName, provider, type)

• tagName - custom element tag name
• provider - plain JS object with lifecycle functions and properties. See under Lifecycle and reserved properties.
• type - optional, function reference to one of htmlhammer's functions (e.q. div, a, table etc.). Use when you want to extend existing html element, e.q. HTMLDivElement.

Lifecycle and reserved properties

• postConstruct
• connectedCallback
• disconnectedCallback
• attributeChangedCallback
• adoptedCallback
• observedAttributes

Differences to the specification:

• postConstruct - think of it as a constructor.
• observedAttributes - an array of strings (names of the observed attributes)

Define custom element

• Using only htmlhammer

const { customElement } = htmlhammer; // or use ES6 import

// Definition
const yetiCustom = customElement('yeti-custom', {
  connectedCallback() {
    console.log('Generic custom element created!');
  }
});

// Usage
document.body.append(yetiCustom());

• Using htmlhammer and html

<script>
  const { customElement } = htmlhammer; // or use ES6 import

  // Definition
  const yetiCustom = customElement('yeti-custom', {
    connectedCallback() {
      console.log('Generic custom element created!');
    }
  });
</script>

<!-- Usage -->
<yeti-custom></yeti-custom>

Extending existing native element

Examples below show how to extend existing HTMLDivElement

• Using only htmlhammer

const { div, customElement } = htmlhammer; // or use ES6 import

// Definition
const yetiDiv = customElement(
  'yeti-div',
  {
    connectedCallback() {
      console.log('Generic custom element created!');
    }
  },
  div
);

// Usage
document.body.append(div({ is: 'yeti-div' }));

• Using htmlhammer and html

<script>
  const { div, customElement } = htmlhammer; // or use ES6 import

  // Definition
  const yetiDiv = customElement(
    'yeti-div',
    {
      connectedCallback() {
        console.log('Generic custom element created!');
      }
    },
    div
  );
</script>

<!-- Usage -->
<div is="yeti-div"></div>

Setting shadow dom

• Inside custom element

const { customElement } = htmlhammer; // or use ES6 import

const yetiCustom = customElement('yeti-custom', {
  connectedCallback() {
    this.attachShadow({ mode: 'open' });
  }
});

• As htmlhammer attribute

yetiCustom(
  { shadowRoot: { mode: 'open' } },
  'Hello from Generic CustomElement'
);

Setting styles

• Inside custom element

const { style, customElement } = htmlhammer; // or use ES6 import

const yetiCustom = customElement('yeti-custom', {
  connectedCallback() {
    this.attachShadow({ mode: 'open' });
    this.shadowRoot.append(style(`:host { font-weight: bold;}`));
  }
});

• As htmlhammer attribute

yetiCustom(
  {
    shadowRoot: {
      mode: 'open',
      stylesheets: [style(`:host {color: red;}`)]
    }
  },
  'Hello from Generic CustomElement'
);

Provider's properties and structured cloning

Properties of provider object(see under Method signature) will be created on each new custom element instance using structuredClone method to ensure that there is no object reference sharing between custom element instances of the same type.

Structured cloning is skipped for functions.

Passing properties

You can pass objects, arrays, functions, class instances and existing dom element references from parent to child element as properties. Numbers, strings dates etc. are treated as attributes. Note that by 'passing' htmlhammer actually creates properties on the object.

// Custom element
let element = customElement('my-element', {
  connectedCallback() {
    console.log(
      this.o,
      this.a,
      this.fn(),
      this.p,
      this.el(),
      this.getAttribute('v'),
      this.getAttribute('s')
    );
  }
});

class Person {}

document.body.append(
  element({
    o: { id: 1 }, // object
    a: [1], // array
    fn: () => 1, // function
    p: new Person(), // instance of class
    el: () => document.getElementById('id'), // dom element reference (pass it as a function)
    v: 1, // number
    s: 'string' // string
  })
);

Conventions

Conventions apply only to the provider(see under Method signature).

• Function starting with capital letter - binds function to context (custom element instance)
• Property starting with capital letter - receives get/set methods
• Property not starting with capital letter - receives only get method
• Property is named the same as observed attribute - property will reflect attribute

Counter web component example

These examples demonstrate how you can use this library to build web component with simple state management and a few action buttons. It also shows you a cool way of how you can set and assign any node you would like to reference at any time during component's life. This feature is basically a consequence of building html with javascript which htmlhammer is all about.

Basic implementation

This example shows how you can create counter web component using dedicated action buttons to change counter's state.

const Counter = customElement('my-counter', {
  Count: 0,
  connectedCallback() {
    this.append(
      button({ id: 'dec', onclick: this.Dec }, '-'),
      (this.CounterDisplay = span(this.Count)), // Cool way to set and assign html element
      button({ id: 'inc', onclick: this.Inc }, '+')
    );
  },
  observedAttributes: ['count'],
  attributeChangedCallback(n, ov, nv) {
    // Each time Count changes a new console log is written
    console.log(`Counter change: ${ov} -> ${nv}`);
  },
  Inc() {
    this.Update(++this.Count);
  },
  Dec() {
    this.Update(--this.Count);
  },
  Update(count) {
    this.CounterDisplay.textContent = count; // Assigned html element referenced
  }
});

Advanced implementation

This example shows how you can create the same counter web component using attributeChangedCallback function to change counter's state.

const Counter = customElement('my-counter-advanced', {
  Count: 0,
  observedAttributes: ['count'],
  attributeChangedCallback(attrName, ov, nv) {
    if (attrName === 'count') {
      this.CounterDisplay.textContent = this.Count;
    }
  },
  connectedCallback() {
    this.attachShadow({ mode: 'open' });
    this.shadowRoot.append(
      button({ id: 'dec', onclick: () => --this.Count }, '-'),
      (this.CounterDisplay = span(this.Count)),
      button({ id: 'inc', onclick: () => ++this.Count }, '+')
    );
  }
});

See both counter web component examples in action by checking live demo.

Live demo

Demo is basically index.html file found in the root of the project served as a github page.

live demo

JSX

As of version 4.0.0 htmlhammer provides experimental JSX support.

hhjsx function

htmlhammer provides hhjsx function which will be used by the compiler to replace JSX elements.

// Below JSX snippet will be replaced by the compiler with hhjsx('a', {anchor: 'anchor'})
<a name="anchor"></a>

hhjsx function can be imported from index.js.

Do note that hhjsx needs to be available to each .js(x) module. Either attach this function to the window when the application is started or import it to each .js(x) module.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta
      name="viewport"
      content="width=device-width, initial-scale=1.0"
    />
    <title>HtmlHammer JSX</title>
  </head>

  <body>
    <script type="module">
      import { hhjsx } from './esm/index.js';
      // Globally available hhjsx function
      // No need for imports in other .js modules using JSX
      window['hhjsx'] = hhjsx;
    </script>
  </body>
</html>

Compiling JSX

In order to use JSX with htmlhammer you need to use a compiler that is able to transform JSX syntax into a function calls. Here, we are using Babel.

Adding Babel support to your project

npm install --save-dev @babel/core @babel/cli @babel/preset-env @babel/preset-react

Adding babel.config.json file to your project

{
  "presets": [
    [
      "@babel/preset-react",
      {
        "pragma": "hhjsx",
        "runtime": "classic"
      }
    ],
    [
      "@babel/preset-env",
      {
        "modules": false
      }
    ]
  ]
}

Example of babel command which compiles all files in the src directory using react and env presets.

# Run compiler from the root of the project
./node_modules/.bin/babel src --out-dir target

Relation of JSX <> (fragment) to htmlhammer's fragment function

Currently, htmlhammer uses <fragment> instead <>.

<fragment>
  <div />
  <div />
</fragment>

// is equivalent to

fragment(
  div(),
  div()
)

Example

You can find an implementation of the working example in the project's demo/jsx directory.

See live demo.

CoffeeScript & htmlhammer

Using CoffeeScript and htmlhammer for creating HTML templates is a great match. If offers visually very expressive form. HTML-like syntax at a reduced cost.

import { div, h1, h2, hr, span, a, br } from "https://unpkg.com/htmlhammer?module"

Movie = ({title, creators, stars, about, imdb}) ->
    [
        h1 title
        hr style:
            height: "2px"
            backgroundColor: "grey"
        h2 "Creators"
        div name for name in creators
        h2 "Info"
        span [
            div "Year: #{about.year}"
            div "Stars: #{about.stars}"
            div "Genres: #{about.genres.join ", "}"
        ]
        h2 "Stars"
        div name for name in stars
        br
        a href: imdb, "IMDb"
    ]

Project's NPM scripts

test - run tests

npm test

coverage - create and print test coverage report to console

npm run coverage

coverage:file - create and print test coverage report to test-coverage-report.txt file

npm run coverage:file

build - build project

npm run build

jsx - compile jsx

npm run jsx

Current version test coverage report

Special thanks

Big thanks to JetBrains for granting me a free license :)