1 files changed, 85 insertions, 0 deletions
diff --git a/src/index.ts b/src/index.ts
new file mode 100644
index 0000000..aa07055
--- /dev/null
+++ b/src/index.ts
@@ -0,0 +1,85 @@
+// An event handler can take an optional event argument
+// and should not return a value
+type EventHandler = (event?: any) => void;
+type WildCardEventHandler = (type: string, event?: any) => void;
+
+// An array of all currently registered event handlers for a type
+type EventHandlerList = Array<EventHandler>;
+type WildCardEventHandlerList = Array<WildCardEventHandler>;
+// A map of event types and their corresponding event handlers.
+type EventHandlerMap = {
+  '*'?: WildCardEventHandlerList;
+  [type: string]: EventHandlerList;
+};
+
+/** Nitt: functional event emitter / pubsub.
+ *  @name nitt
+ *  @returns {Nitt}
+ */
+export default function nitt(all: EventHandlerMap) {
+  all = all || Object.create(null);
+
+  return {
+    /**
+     * Register an event handler for the given type.
+     *
+     * @param  {String} type	Type of event to listen for, or `"*"` for all events
+     * @param  {Function} handler Function to call in response to given event
+     */
+    on(type: string, handler: EventHandler) {
+      (all[type] || (all[type] = [])).push(handler);
+    },
+
+    /**
+     * Register an event handler that is executed just once.
+     *
+     * @param  {String} type	Type of event to listen for, or `"*"` for any event
+     * @param  {Function} handler Function to call in response to given event
+     */
+    once(type: string, handler: EventHandler) {
+      const onceHandler = evt => {
+        handler(evt);
+        this.off(type, onceHandler);
+      };
+      this.on(type, onceHandler);
+    },
+
+    /**
+     * Returns a promise for a single event
+     *
+     * @param  {String} type	Type of event to listen for, or `"*"` for any event
+     * @returns {Promise<any>}
+     */
+    when(type: string): Promise<any> {
+      return new Promise<any>(r => this.once(type, r));
+    },
+
+    /**
+     * Remove an event handler for the given type.
+     *
+     * @param  {String} type	Type of event to unregister `handler` from, or `"*"`
+     * @param  {Function} handler Handler function to remove
+     */
+    off(type: string, handler: EventHandler) {
+      if (all[type]) {
+        all[type].splice(all[type].indexOf(handler) >>> 0, 1);
+      }
+    },
+
+    /**
+     * Invoke all handlers for the given type.
+     * If present, `"*"` handlers are invoked after type-matched handlers.
+     *
+     * @param {String} type  The event type to invoke
+     * @param {Any} [evt]  Any value (object is recommended and powerful), passed to each handler
+     */
+    emit(type: string, evt: any) {
+      (all[type] || []).forEach(handler => {
+        handler(evt);
+      });
+      (all['*'] || []).forEach(handler => {
+        handler(type, evt);
+      });
+    },
+  };
+}