svelte/packages/svelte/src/internal/client/dom/elements/events.js

import { teardown } from '../../reactivity/effects.js';
import { define_property, is_array } from '../../../shared/utils.js';
import { hydrating } from '../hydration.js';
import { queue_micro_task } from '../task.js';
import { FILENAME } from '../../../../constants.js';
import * as w from '../../warnings.js';
import {
	active_effect,
	active_reaction,
	set_active_effect,
	set_active_reaction
} from '../../runtime.js';
import { without_reactive_context } from './bindings/shared.js';

/** @type {Set<string>} */
export const all_registered_events = new Set();

/** @type {Set<(events: Array<string>) => void>} */
export const root_event_handles = new Set();

/**
 * SSR adds onload and onerror attributes to catch those events before the hydration.
 * This function detects those cases, removes the attributes and replays the events.
 * @param {HTMLElement} dom
 */
export function replay_events(dom) {
	if (!hydrating) return;

	dom.removeAttribute('onload');
	dom.removeAttribute('onerror');
	// @ts-expect-error
	const event = dom.__e;
	if (event !== undefined) {
		// @ts-expect-error
		dom.__e = undefined;
		queueMicrotask(() => {
			if (dom.isConnected) {
				dom.dispatchEvent(event);
			}
		});
	}
}

/**
 * @param {string} event_name
 * @param {EventTarget} dom
 * @param {EventListener} [handler]
 * @param {AddEventListenerOptions} [options]
 */
export function create_event(event_name, dom, handler, options = {}) {
	/**
	 * @this {EventTarget}
	 */
	function target_handler(/** @type {Event} */ event) {
		if (!options.capture) {
			// Only call in the bubble phase, else delegated events would be called before the capturing events
			handle_event_propagation.call(dom, event);
		}

		// @ts-expect-error Use this instead of cancelBubble, because cancelBubble is also true if
		// we're the last element on which the event will be handled.
		if (!event.__cancelled || event.__cancelled === dom) {
			return without_reactive_context(() => {
				return handler?.call(this, event);
			});
		}
	}

	// Chrome has a bug where pointer events don't work when attached to a DOM element that has been cloned
	// with cloneNode() and the DOM element is disconnected from the document. To ensure the event works, we
	// defer the attachment till after it's been appended to the document. TODO: remove this once Chrome fixes
	// this bug. The same applies to wheel events and touch events.
	if (
		event_name.startsWith('pointer') ||
		event_name.startsWith('touch') ||
		event_name === 'wheel'
	) {
		queue_micro_task(() => {
			dom.addEventListener(event_name, target_handler, options);
		});
	} else {
		dom.addEventListener(event_name, target_handler, options);
	}

	return target_handler;
}

/**
 * Attaches an event handler to an element and returns a function that removes the handler. Using this
 * rather than `addEventListener` will preserve the correct order relative to handlers added declaratively
 * (with attributes like `onclick`), which use event delegation for performance reasons
 *
 * @param {EventTarget} element
 * @param {string} type
 * @param {EventListener} handler
 * @param {AddEventListenerOptions} [options]
 */
export function on(element, type, handler, options = {}) {
	var target_handler = create_event(type, element, handler, options);

	return () => {
		element.removeEventListener(type, target_handler, options);
	};
}

/**
 * @param {string} event_name
 * @param {Element} dom
 * @param {EventListener} [handler]
 * @param {boolean} [capture]
 * @param {boolean} [passive]
 * @returns {void}
 */
export function event(event_name, dom, handler, capture, passive) {
	var options = { capture, passive };
	var target_handler = create_event(event_name, dom, handler, options);

	if (
		dom === document.body ||
		// @ts-ignore
		dom === window ||
		// @ts-ignore
		dom === document ||
		// Firefox has quirky behavior, it can happen that we still get "canplay" events when the element is already removed
		dom instanceof HTMLMediaElement
	) {
		teardown(() => {
			dom.removeEventListener(event_name, target_handler, options);
		});
	}
}

/**
 * @param {Array<string>} events
 * @returns {void}
 */
export function delegate(events) {
	for (var i = 0; i < events.length; i++) {
		all_registered_events.add(events[i]);
	}

	for (var fn of root_event_handles) {
		fn(events);
	}
}

// used to store the reference to the currently propagated event
// to prevent garbage collection between microtasks in Firefox
// If the event object is GCed too early, the expando __root property
// set on the event object is lost, causing the event delegation
// to process the event twice
let last_propagated_event = null;

/**
 * @this {EventTarget}
 * @param {Event} event
 * @returns {void}
 */
export function handle_event_propagation(event) {
	var handler_element = this;
	var owner_document = /** @type {Node} */ (handler_element).ownerDocument;
	var event_name = event.type;
	var path = event.composedPath?.() || [];
	var current_target = /** @type {null | Element} */ (path[0] || event.target);

	last_propagated_event = event;

	// composedPath contains list of nodes the event has propagated through.
	// We check __root to skip all nodes below it in case this is a
	// parent of the __root node, which indicates that there's nested
	// mounted apps. In this case we don't want to trigger events multiple times.
	var path_idx = 0;

	// the `last_propagated_event === event` check is redundant, but
	// without it the variable will be DCE'd and things will
	// fail mysteriously in Firefox
	// @ts-expect-error is added below
	var handled_at = last_propagated_event === event && event.__root;

	if (handled_at) {
		var at_idx = path.indexOf(handled_at);
		if (
			at_idx !== -1 &&
			(handler_element === document || handler_element === /** @type {any} */ (window))
		) {
			// This is the fallback document listener or a window listener, but the event was already handled
			// -> ignore, but set handle_at to document/window so that we're resetting the event
			// chain in case someone manually dispatches the same event object again.
			// @ts-expect-error
			event.__root = handler_element;
			// @ts-expect-error
			event.__cancelled = null;
			return;
		}

		// We're deliberately not skipping if the index is higher, because
		// someone could create an event programmatically and emit it multiple times,
		// in which case we want to handle the whole propagation chain properly each time.
		// (this will only be a false negative if the event is dispatched multiple times and
		// the fallback document listener isn't reached in between, but that's super rare)
		var handler_idx = path.indexOf(handler_element);
		if (handler_idx === -1) {
			// handle_idx can theoretically be -1 (happened in some JSDOM testing scenarios with an event listener on the window object)
			// so guard against that, too, and assume that everything was handled at this point.
			return;
		}

		if (at_idx <= handler_idx) {
			path_idx = at_idx;
		}
	}

	current_target = /** @type {Element} */ (path[path_idx] || event.target);
	// there can only be one delegated event per element, and we either already handled the current target,
	// or this is the very first target in the chain which has a non-delegated listener, in which case it's safe
	// to handle a possible delegated event on it later (through the root delegation listener for example).
	if (current_target === handler_element) return;

	// Proxy currentTarget to correct target
	define_property(event, 'currentTarget', {
		configurable: true,
		get() {
			return current_target || owner_document;
		}
	});

	// This started because of Chromium issue https://chromestatus.com/feature/5128696823545856,
	// where removal or moving of of the DOM can cause sync `blur` events to fire, which can cause logic
	// to run inside the current `active_reaction`, which isn't what we want at all. However, on reflection,
	// it's probably best that all event handled by Svelte have this behaviour, as we don't really want
	// an event handler to run in the context of another reaction or effect.
	var previous_reaction = active_reaction;
	var previous_effect = active_effect;
	set_active_reaction(null);
	set_active_effect(null);

	try {
		var cancelled = event.cancelBubble;
		/**
		 * @type {unknown}
		 */
		var throw_error;
		/**
		 * @type {unknown[]}
		 */
		var other_errors = [];

		while (current_target !== null) {
			/** @type {null | Element} */
			var parent_element =
				current_target.assignedSlot ||
				current_target.parentNode ||
				/** @type {any} */ (current_target).host ||
				null;

			try {
				// @ts-expect-error
				var delegated = current_target['__' + event_name];

				if (
					delegated != null &&
					(!(/** @type {any} */ (current_target).disabled) ||
						// DOM could've been updated already by the time this is reached, so we check this as well
						// -> the target could not have been disabled because it emits the event in the first place
						event.target === current_target)
				) {
					if (is_array(delegated)) {
						var [fn, ...data] = delegated;
						fn.apply(current_target, [event, ...data]);
					} else {
						delegated.call(current_target, event);
					}
				}
			} catch (error) {
				if (throw_error) {
					other_errors.push(error);
				} else {
					throw_error = error;
				}
			}
			if (event.cancelBubble || parent_element === handler_element || parent_element === null) {
				if (!cancelled && event.cancelBubble) {
					// @ts-expect-error
					event.__cancelled = current_target;
				}
				break;
			}
			current_target = parent_element;
		}

		if (throw_error) {
			for (let error of other_errors) {
				// Throw the rest of the errors, one-by-one on a microtask
				queueMicrotask(() => {
					throw error;
				});
			}
			throw throw_error;
		}
	} finally {
		// @ts-expect-error is used above
		event.__root = handler_element;
		// @ts-ignore remove proxy on currentTarget
		delete event.currentTarget;
		set_active_reaction(previous_reaction);
		set_active_effect(previous_effect);
	}
}

/**
 * In dev, warn if an event handler is not a function, as it means the
 * user probably called the handler or forgot to add a `() =>`
 * @param {() => (event: Event, ...args: any) => void} thunk
 * @param {EventTarget} element
 * @param {[Event, ...any]} args
 * @param {any} component
 * @param {[number, number]} [loc]
 * @param {boolean} [remove_parens]
 */
export function apply(
	thunk,
	element,
	args,
	component,
	loc,
	has_side_effects = false,
	remove_parens = false
) {
	let handler;
	let error;

	try {
		handler = thunk();
	} catch (e) {
		error = e;
	}

	if (typeof handler !== 'function' && (has_side_effects || handler != null || error)) {
		const filename = component?.[FILENAME];
		const location = loc ? ` at ${filename}:${loc[0]}:${loc[1]}` : ` in ${filename}`;
		const phase = args[0]?.eventPhase < Event.BUBBLING_PHASE ? 'capture' : '';
		const event_name = args[0]?.type + phase;
		const description = `\`${event_name}\` handler${location}`;
		const suggestion = remove_parens ? 'remove the trailing `()`' : 'add a leading `() =>`';

		w.event_handler_invalid(description, suggestion);

		if (error) {
			throw error;
		}
	}
	handler?.apply(element, args);
}