CODEWITHSUNDEEP
javascriptweb-componentshadow-domcustom-element
asv
asv

Reputation: 3792

User's style for vanilla JS webcomponent

I have this component:

index.html

<html>

<head>
    <title></title>
    <meta charset="UTF-8">
    <script src="clock.js"></script>
    <style>
        clock-digital div {
            background-color: green;
        }
    </style>
</head>

<body>
    <clock-digital></clock-digital>
</body>

</html>

clock.js

customElements.define('clock-digital', class extends HTMLElement {

    constructor() {
        super();
        var shadowRoot = this.attachShadow({
            mode: 'open'
        });
        this._clockID = setInterval(function () {
            var currentdate = new Date();
            var hours = ( (currentdate.getHours() < 10) ? '0' : '') + currentdate.getHours();
            var minutes = ( (currentdate.getMinutes() < 10) ? '0' : '') + currentdate.getMinutes();
            var seconds = ( (currentdate.getSeconds() < 10) ? '0' : '') + currentdate.getSeconds();
            shadowRoot.innerHTML = `
            <style>
                div {
                    display: inline-block;
                    width: 65px;
                    text-align: center;
                    background-color: whitesmoke;
                    font-style: italic;
                    border: 1px solid lightgray;
                    border-radius: 3px;
                    box-shadow: 2px 2px 3px;
                }
            </style>
            <div>
                ${hours}:${minutes}:${seconds}
            </div>`;
        }, 500);
    }

});

I want that user of component can define his style on clock. I tried with:

<style>
        clock-digital div {
            background-color: green;
        }
    </style>

but it doesn't work. Should I use the slot tag somewhere in shadow root? What is best practice to achieve that?

Upvotes: 1

Views: 507

Answers (2)

Supersharp
Supersharp

Reputation: 31171

You can also take profit of the priority of the user defined CSS rules over the :host selector that represents the Shadow DOM root (i.e. the custom element itself).

In your custom element, use :host to style the content:

shadowRoot.innerHTML = `
    <style>
        :host {
            display: inline-block;
            width: 65px;
            text-align: center;
            background-color: whitesmoke;
            font-style: italic;
            border: 1px solid lightgray;
            border-radius: 3px;
            box-shadow: 2px 2px 3px;
        }
    </style>
    <div>
        ${hours}:${minutes}:${seconds}
    </div>`

Now the user can define its own styles with standard CSS notation, like for any HTML elements. This will override the styles defined by the :host rule.

<style>
     clock-digital {
         background-color: green;
         color: white;
     }
</style>


customElements.define('clock-digital', class extends HTMLElement {
    constructor() {
        super();
        var shadowRoot = this.attachShadow({ mode: 'open' });
        this._clockID = setInterval(function () {
            var currentdate = new Date();
            var hours = ('0'+currentdate.getHours()).substr(-2,2)
            var minutes = ('0'+currentdate.getMinutes()).substr(-2,2)
            var seconds = ('0'+currentdate.getSeconds()).substr(-2,2) 
            shadowRoot.innerHTML = `
            <style>
                :host {
                    display: inline-block;
                    width: 65px;
                    text-align: center;
                    background-color: whitesmoke;
                    font-style: italic;
                    border: 1px solid lightgray;
                    border-radius: 3px;
                    box-shadow: 2px 2px 3px;
                }
            </style>           
            ${hours}:${minutes}:${seconds}`;
        }, 500);
    }
});
clock-digital  {
  background-color: green;
  color: white;
  font-weight: bold;
}
<clock-digital></clock-digital>

Upvotes: 2

tony19
tony19

Reputation: 138276

You could expose CSS properties in your custom element that could be set externally.

In your example, your element could define --clock-background-color, which sets the div's background color:

shadowRoot.innerHTML = 
  `<style>
     div {
       background-color: var(--clock-background-color, whitesmoke);
       /* ... */
     }
   </style>
   <div>
     ${hours}:${minutes}:${seconds}
   </div>`;

Then, your element's users could change the background color to green with this:

<style>
  clock-digital {
    --clock-background-color: green;
  }
</style>
<clock-digital></clock-digital>

codepen

Note the Codepen demo uses Web Components polyfills for non-Chrome browsers, but you can comment it out to see that it still works vanilla in Chrome.

Upvotes: 2

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