Merge pull request #498 from atomiks/eventhub

[FEATURE] Add createEventHub

snippets/createEventHub.md

@@ -0,0 +1,45 @@
+### createEventHub
+
+Creates a pub/sub ([publish–subscribe](https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern)) event hub with `emit`, `on`, and `off` methods.
+
+Use `Object.create(null)` to create an empty `hub` object that does not inherit properties from `Object.prototype`.
+For `emit`, resolve the array of handlers based on the `event` argument and then run each one with `Array.forEach()` by passing in the data as an argument.
+For `on`, create an array for the event if it does not yet exist, then use `Array.push()` to add the handler
+to the array.
+For `off`, use `Array.findIndex()` to find the index of the handler in the event array and remove it using `Array.splice()`.
+
+```js
+const createEventHub = () => ({
+  hub: Object.create(null),
+  emit(event, data) {
+    (this.hub[event] || []).forEach(handler => handler(data));
+  },
+  on(event, handler) {
+    if (!this.hub[event]) this.hub[event] = [];
+    this.hub[event].push(handler);
+  },
+  off(event, handler) {
+    const i = (this.hub[event] || []).findIndex(h => h === handler);
+    if (i > -1) this.hub[event].splice(i, 1);
+  }
+});
+```
+
+```js
+const handler = data => console.log(data);
+const hub = createEventHub();
+let increment = 0;
+
+// Subscribe: listen for different types of events
+hub.on('message', handler);
+hub.on('message', () => console.log('Message event fired'));
+hub.on('increment', () => increment++);
+
+// Publish: emit events to invoke all handlers subscribed to them, passing the data to them as an argument
+hub.emit('message', 'hello world'); // logs 'hello world' and 'Message event fired'
+hub.emit('message', { hello: 'world' }); // logs the object and 'Message event fired'
+hub.emit('increment'); // `increment` variable is now 1
+
+// Unsubscribe: stop a specific handler from listening to the 'message' event
+hub.off('message', handler); 
+```

tag_database

@@ -22,6 +22,7 @@ countVowels:string
 createElement:browser,utility
 currentURL:browser,url
 curry:function,recursion
+createEventHub:browser,event,advanced
 deepFlatten:array,recursion
 defer:function
 detectDeviceType:browser