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

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- 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

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npm i htmlhammer

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``html














`

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

Importing and using htmlhammer

`javascript
// In html
;
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

`javascript
// 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.

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`javascript
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)))
)
);
`

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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).

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

const html = '

Hello World!

';

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.

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

document.body.append(
div(span({ $apply: RawHtml('

Hello World!

') }))
);
`

For more complex and complete examples see demo.

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#### $for - creating multiple elements of the same type

`javascript
// Creates three elements of type div,

,

2

,

3

// 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

`javascript
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!

`javascript
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.

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

// Function which can replace new HtmlString("

Hello

")
const HTMLContent = data => el => (el.innerHTML = data);

// Valid usages
div({ $apply: RedText });
div({ $apply: [RedText, HTMLContent('

Hello

')] });
`

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

`javascript
// 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');
`

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

`javascript
// 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.

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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.

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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

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

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

Custom elements

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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.

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- 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)

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- Using only htmlhammer

`javascript
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

`html




`

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Examples below show how to extend existing HTMLDivElement

- Using only htmlhammer

`javascript
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

`html






`

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- Inside custom element

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

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

- As htmlhammer attribute

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

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- Inside custom element

`javascript
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

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

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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.

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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.

`javascript
// 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
})
);
`

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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

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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.

`javascript
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.

`javascript
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.

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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.

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

`js Example
// Below JSX snippet will be replaced by the compiler with hhjsx('a', {anchor: 'anchor'})

`

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.

`html




name="viewport"
content="width=device-width, initial-scale=1.0"
/>







`

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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

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

#### Adding babel.config.json file to your project

`json
{
"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.

`bash


Run compiler from the root of the project


./node_modules/.bin/babel src --out-dir target
`

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Currently, htmlhammer uses \ instead <>.

`js