@marcoms/make-element

Create custom elements without boilerplate

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Readme

make-element

make-element provides a simple and ergonomic system for creating Web Components. It is lightweight, imperative1, supports Shadow DOM, and supports property/attribute binding.

Example

JS

const CounterElement = makeElement({
    props: {
        counter: {
            init: 1,
            set(counter) {
                this.$['counter'].textContent = counter;
            },
        },
    },

    methods: {
        increment() {
            ++this.counter;
        },
    },

    ready() {
        this.$['increment-button'].onclick = () => {
            this.increment()
        };
    },

    shadowDom: true,
    template: `
        <div id="counter"></div>
        <button id="increment-button">Increment</button>
    `,
});

customElements.define('counter-element', CounterElement);

HTML

<counter-element></counter-element>

Result

Counter demo

API

makeElement(definition={})

Produces a custom element class that can be passed to customElements.define.

props

Collection of properties to register for the custom element. All configuration fields (attr, get, set, …) are optional

init

Initial value of the property to use, unless the property is bound to an attribute with attr (e.g. attr: 'foo') and initialized in markup (e.g. <x-element foo="24"></x-element>)

attr

Default: (none)

Attribute name to bind to

Every time the property is set, the value will flow into the attribute name specified here via coerce(), then toAttr()

A property can be initialised through markup by supplying an attribute value, but subsequent changes to the attribute will not flow back to the property -- binding is therefore one-way from property to attribute

Example
myProp: {
    attr: 'my-attr',
}
<my-element my-attr="24"></my-element>
myElement.myProp;  // -> 24 (initialised from attribute)

myElement.myProp = 32;
myElement.getAttribute('my-attr');  // -> 32 (flowed from property)

myElement.setAttribute('my-attr', 48);
myElement.myProp;  // -> 32 (no change)
boolAttr

Whether the attribute is a boolean attribute

Boolean attributes automatically have defined a toAttr function that returns '' (making the attribute true) on a truthy value and undefined (removing the attribute) on a falsy value.

get(val)

Getter function called when the property is accessed

Example
get(fullName) {
    const [firstName, lastName] = fullName.split(' ');
    return {firstName, lastName};
}
set(val)

Setter function called on every update to the property value

Example
set(val) {
    console.log('property was set to', val);
}
coerce(val)

Function used to modify the property value before it is stored and passed to set()

Example
coerce(val) {
    return Number.parseInt(val, 10);
}
toAttr(val)

Function used to modify the property value when storing into an attribute

Return values of undefined will remove the attribute

fromAttr(val)

Function used to modify the attribute value if the property is initialized from the attribute

methods

Collection of methods to assign to the custom element prototype

Example
methods: {
    myMethod() {
        console.log('hello from myMethod');
    },
}
myElement.myMethod();  // -> hello from myMethod

shadowDom

Default: false

If true, shadow DOM will be used for templating

See http://caniuse.com/#feat=shadowdomv1

template

HTML template to initialise the custom element with

If templateUrl is also defined, template will be used

templateUrl

Like template, but fetches the template from this URL

If template is also defined, template will be used

cacheIds

Default: true

If true, elements in the template with an id attribute will be stored in the $ property for easy and fast referencing.

Example
cacheIds: true,
template: `<p id="hello">hello</p>`,

ready() {
    this.$['hello'].onclick = () => {
        console.log('hello');
    };
},

ready()

Function invoked once the custom element has initialised its template and connected to the DOM

License

MIT (see license.txt)

Notes

1: For a functional-style custom elements library, see skatejs

If you find any bugs or have a feature request, please open an issue on github!

The npm package download data comes from npm's download counts api and package details come from npms.io.