@sandlada/vue-mdc/src/internals/events/form-label-activation.ts


/**
 * @license
 * Copyright 2021 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 * 
 * @link https://github.com/material-components/material-web/blob/main/internal/events/form-label-activation.ts
 */

/**
 * Dispatches a click event to the given element that triggers a native action,
 * but is not composed and therefore is not seen outside the element.
 *
 * This is useful for responding to an external click event on the host element
 * that should trigger an internal action like a button click.
 *
 * Note, a helper is provided because setting this up correctly is a bit tricky.
 * In particular, calling `click` on an element creates a composed event, which
 * is not desirable, and a manually dispatched event must specifically be a
 * `MouseEvent` to trigger a native action.
 *
 * @example
 * hostClickListener = (event: MouseEvent) {
 *   if (isActivationClick(event)) {
 *     this.dispatchActivationClick(this.buttonElement);
 *   }
 * }
 *
 */
export function dispatchActivationClick(element: HTMLElement) {
    const event = new MouseEvent('click', { bubbles: true })
    element.dispatchEvent(event)
    return event
}

/**
 * Returns true if the click event should trigger an activation behavior. The
 * behavior is defined by the element and is whatever it should do when
 * clicked.
 *
 * Typically when an element needs to handle a click, the click is generated
 * from within the element and an event listener within the element implements
 * the needed behavior; however, it's possible to fire a click directly
 * at the element that the element should handle. This method helps
 * distinguish these "external" clicks.
 *
 * An "external" click can be triggered in a number of ways: via a click
 * on an associated label for a form  associated element, calling
 * `element.click()`, or calling
 * `element.dispatchEvent(new MouseEvent('click', ...))`.
 *
 * Also works around Firefox issue
 * https://bugzilla.mozilla.org/show_bug.cgi?id=1804576 by squelching
 * events for a microtask after called.
 *
 * @example
 * hostClickListener = (event: MouseEvent) {
 *   if (isActivationClick(event)) {
 *     this.dispatchActivationClick(this.buttonElement);
 *   }
 * }
 *
 */
export function isActivationClick(event: Event) {
    // Event must start at the event target.
    if (event.currentTarget !== event.target) {
        return false
    }
    // Event must not be retargeted from shadowRoot.
    if (event.composedPath()[0] !== event.target) {
        return false
    }
    // Target must not be disabled; this should only occur for a synthetically
    // dispatched click.
    if ((event.target as EventTarget & { disabled: boolean }).disabled) {
        return false
    }
    // This is an activation if the event should not be squelched.
    return !squelchEvent(event)
}

// TODO(https://bugzilla.mozilla.org/show_bug.cgi?id=1804576)
//  Remove when Firefox bug is addressed.
function squelchEvent(event: Event) {
    const squelched = isSquelchingEvents
    if (squelched) {
        event.preventDefault()
        event.stopImmediatePropagation()
    }
    squelchEventsForMicrotask()
    return squelched
}

// Ignore events for one microtask only.
let isSquelchingEvents = false
async function squelchEventsForMicrotask() {
    isSquelchingEvents = true
    // Need to pause for just one microtask.
    // tslint:disable-next-line
    await null
    isSquelchingEvents = false
}