Using a Material Web Component inside a litElement

Question

I'm trying to make a small app using the PWA Starter Kit from the Polymer project.

Is it possible to use a web component from https://material.io/develop/web/components/input-controls/text-field/ inside my LitElement? I want use a text area.

What I have tried:

import {html, customElement, LitElement} from "lit-element";
//
import {MDCTextField} from '@material/textfield';

@customElement('text-editor')
export class TextEditor extends LitElement {

    protected render() {
        return html`<div class="mdc-text-field mdc-text-field--textarea">
  <textarea id="textarea" class="mdc-text-field__input" rows="8" cols="40"></textarea>
  <div class="mdc-notched-outline">
    <div class="mdc-notched-outline__leading"></div>
    <div class="mdc-notched-outline__notch">
      <label for="textarea" class="mdc-floating-label">Textarea Label</label>
    </div>
    <div class="mdc-notched-outline__trailing"></div>
  </div>
</div>`
    }

}

However, because I don't use "MDCTextField" anywhere, the TypeScript compiler complains that "'MDCTextField' is declared but its value is never read.".

I do get a text area rendered in the HTML, but none of the styles are applied.

How can I reuse the MDCTextField web component in a LitElement?

Answer 1

Yes, you have to use LitElement's static styles which uses Constructible styles along with fallback for non-supporting browsers:

import { html, customElement, LitElement, unsafeCSS } from 'lit-element';

import { MDCTextField } from '@material/textfield';

// IMPORTANT: USE WEBPACK RAW-LOADER OR EQUIVALENT
import style from 'raw-loader!@material/textfield/dist/mdc.textfield.css';

@customElement('text-editor')
export class TextEditor extends LitElement {

  static styles = [unsafeCSS(style)];

  private textField?: MDCTextField;

  connectedCallback() {

    super.connectedCallback();

    const elm = this.shadowRoot!.querySelector('.mdc-text-field')! as HTMLElement;

    if (elm && !this.textField) {
      // Element is re-attached to the DOM
      this.makeTextField();
    }
  }

  disconnectedCallback() {
    if (this.textField) {
      this.textField.destroy();
      this.textField = undefined;
    }
  }

  render() {
    return html`
      <div class='mdc-text-field mdc-text-field--textarea'>
        <textarea id='textarea' class='mdc-text-field__input' rows='8' cols='40'></textarea>
        <div class='mdc-notched-outline'>
          <div class='mdc-notched-outline__leading'></div>
          <div class='mdc-notched-outline__notch'>
            <label for='textarea' class='mdc-floating-label'>Textarea Label</label>
          </div>
          <div class='mdc-notched-outline__trailing'></div>
        </div>
    </div>`;
  }

  firstUpdated() {
    // Executed just once
    this.makeTextField();
  }

  private makeTextField() {
    const elm = this.shadowRoot!.querySelector('.mdc-text-field')! as HTMLElement;

    this.textField = new MDCTextField(elm);
  }

}

These are the things you need to do:

1. Use a bundler like Webpack or rollup to read CSS file as a string. In the above example, I used Sebpack with raw-loader.
2. Initialize MDCTextField when the component is rendered for the first time using firstUpdated lifecycle event.
3. Subsequently, a component may be removed and re-inserted into the DOM and thus you will want to destroy, cleanup and re-initialize the MDCTextField instance.