95 lines
2.2 KiB
JavaScript
95 lines
2.2 KiB
JavaScript
/**
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* An event hub with a Vue instance like API
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*
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* NOTE: This is a derivative work from [mitt][1] v1.2.0 which is licensed by
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* [MIT License][2] © [Jason Miller][3]
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*
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* [1]: https://github.com/developit/mitt
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* [2]: https://opensource.org/licenses/MIT
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* [3]: https://jasonformat.com/
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*/
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class EventHub {
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constructor() {
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this.$_all = new Map();
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}
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dispose() {
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this.$_all.clear();
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}
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/**
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* Register an event handler for the given type.
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*
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* @param {string|symbol} type Type of event to listen for
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* @param {Function} handler Function to call in response to given event
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*/
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$on(type, handler) {
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const handlers = this.$_all.get(type);
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const added = handlers && handlers.push(handler);
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if (!added) {
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this.$_all.set(type, [handler]);
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}
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}
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/**
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* Remove an event handler or all handlers for the given type.
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*
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* @param {string|symbol} type Type of event to unregister `handler`
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* @param {Function} handler Handler function to remove
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*/
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$off(type, handler) {
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const handlers = this.$_all.get(type) || [];
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const newHandlers = handler ? handlers.filter((x) => x !== handler) : [];
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if (newHandlers.length) {
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this.$_all.set(type, newHandlers);
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} else {
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this.$_all.delete(type);
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}
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}
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/**
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* Add an event listener to type but only trigger it once
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*
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* @param {string|symbol} type Type of event to listen for
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* @param {Function} handler Handler function to call in response to event
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*/
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$once(type, handler) {
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const wrapHandler = (...args) => {
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this.$off(type, wrapHandler);
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handler(...args);
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};
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this.$on(type, wrapHandler);
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}
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/**
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* Invoke all handlers for the given type.
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*
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* @param {string|symbol} type The event type to invoke
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* @param {Any} [evt] Any value passed to each handler
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*/
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$emit(type, ...args) {
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const handlers = this.$_all.get(type) || [];
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handlers.forEach((handler) => {
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handler(...args);
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});
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}
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}
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/**
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* Return a Vue like event hub
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*
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* - $on
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* - $off
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* - $once
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* - $emit
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*
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* We'd like to shy away from using a full fledged Vue instance from this in the future.
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*/
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export default () => {
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return new EventHub();
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};
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