static_src/elements/chops/chops-toggle/chops-toggle.js

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

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

/**
 * `<chops-toggle>`
 *
 * A toggle button component. This component is primarily a wrapper
 * around a native checkbox to allow easy sharing of styles.
 *
 */
export class ChopsToggle extends LitElement {
  /** @override */
  static get styles() {
    return css`
      :host {
        --chops-toggle-bg: none;
        --chops-toggle-color: var(--chops-primary-font-color);
        --chops-toggle-hover-bg: rgba(0, 0, 0, 0.3);
        --chops-toggle-focus-border: hsl(193, 82%, 63%);
        --chops-toggle-checked-bg: rgba(0, 0, 0, 0.6);
        --chops-toggle-checked-color: var(--chops-white);
      }
      label {
        background: var(--chops-toggle-bg);
        color: var(--chops-toggle-color);
        cursor: pointer;
        align-items: center;
        padding: 2px 4px;
        border: var(--chops-normal-border);
        border-radius: var(--chops-button-radius);
      }
      input[type="checkbox"] {
        /* We need the checkbox to be hidden but still accessible. */
        opacity: 0;
        width: 0;
        height: 0;
        position: absolute;
        top: -9999;
        left: -9999;
      }
      input[type="checkbox"]:focus + label {
        /* Make sure an outline shows around this element for
        * accessibility.
        */
        box-shadow: 0 0 5px 1px var(--chops-toggle-focus-border);
      }
      input[type="checkbox"]:hover + label {
        background: var(--chops-toggle-hover-bg);
      }
      input[type="checkbox"]:checked + label {
        background: var(--chops-toggle-checked-bg);
        color: var(--chops-toggle-checked-color);
      }
      input[type="checkbox"]:disabled + label {
        opacity: 0.8;
        cursor: default;
        pointer-events: none;
      }
    `;
  }

  /** @override */
  render() {
    return html`
      <input id="checkbox"
        type="checkbox"
        ?checked=${this.checked}
        ?disabled=${this.disabled}
        @change=${this._checkedChangeHandler}
      >
      <label for="checkbox">
        <slot></slot>
      </label>
    `;
  }

  /** @override */
  static get properties() {
    return {
      /**
       * Note: At the moment, this component does not manage its own
       * internal checked state. It expects its checked state to come
       * from its parent, and its parent is expected to update the
       * chops-checkbox's checked state on a change event.
       *
       * This can be generalized in the future to support multiple
       * ways of managing checked state if needed.
       **/
      checked: {type: Boolean},
      /**
       * Whether the element currently allows checking or not.
       */
      disabled: {type: Boolean},
    };
  }

  click() {
    super.click();
    this.shadowRoot.querySelector('#checkbox').click();
  }

  _checkedChangeHandler(evt) {
    this._checkedChange(evt.target.checked);
  }

  /**
   * @param {boolean} checked
   * @fires CustomEvent#checked-change
   * @private
   */
  _checkedChange(checked) {
    if (checked === this.checked) return;
    const customEvent = new CustomEvent('checked-change', {
      detail: {
        checked: checked,
      },
    });
    this.dispatchEvent(customEvent);
  }
}
customElements.define('chops-toggle', ChopsToggle);