// @flow
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// An event handler can take an optional event argument
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// and should not return a value
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type EventHandler = (event?: any) => void;
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// An array of all currently registered event handlers for a type
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type EventHandlerList = Array<EventHandler>;
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// A map of event types and their corresponding event handlers.
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type EventHandlerMap = {
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[type: string]: EventHandlerList,
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};
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/** Mitt: Tiny (~200b) functional event emitter / pubsub.
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* @name mitt
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* @returns {Mitt}
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*/
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export default function mitt(all: EventHandlerMap) {
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all = all || Object.create(null);
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return {
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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} type Type of event to listen for, or `"*"` for all events
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* @param {Function} handler Function to call in response to given event
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* @memberOf mitt
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*/
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on(type: string, handler: EventHandler) {
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(all[type] || (all[type] = [])).push(handler);
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},
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/**
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* Remove an event handler for the given type.
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*
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* @param {String} type Type of event to unregister `handler` from, or `"*"`
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* @param {Function} handler Handler function to remove
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* @memberOf mitt
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*/
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off(type: string, handler: EventHandler) {
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if (all[type]) {
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all[type].splice(all[type].indexOf(handler) >>> 0, 1);
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}
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},
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/**
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* Invoke all handlers for the given type.
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* If present, `"*"` handlers are invoked after type-matched handlers.
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*
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* @param {String} type The event type to invoke
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* @param {Any} [evt] Any value (object is recommended and powerful), passed to each handler
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* @memberof mitt
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*/
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emit(type: string, evt: any) {
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(all[type] || []).map((handler) => { handler(evt); });
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(all['*'] || []).map((handler) => { handler(type, evt); });
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}
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};
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}
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