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Node.js/Standard Packages/events.md

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+# Events Module
+
+Much of the Node.js core API is built around an idiomatic *asynchronous event-driven architecture* in which certain kinds of objects (**emitters**) emit *named events* that cause `Function` objects (**listeners**) to be called.
+
+All objects that emit events are instances of the `EventEmitter` class. These objects expose an `eventEmitter.on()` function that allows one or more functions to be attached to named events emitted by the object. Typically, event names are camel-cased strings but any valid JavaScript property key can be used.
+
+When the EventEmitter object emits an event, all of the functions attached to that specific event are called *synchronously*. Any values returned by the called listeners are *ignored and discarded*.
+
+```js
+const EventEmitter = require("events");
+
+class CustomEmitter extends EventEmitter {} ;
+
+const customEmitterObj = new CustomEmitter();
+
+// add event listener
+cusomEmitterObj.on("event", (e) => {
+    // e contains event object
+})
+
+// single-use event listener (execute and remove listener)
+cusomEmitterObj.once("event", (e) => {
+    // e contains event object
+})
+
+customEmitterObj.removeListener("event", callback);
+customEmitterObj.removeAllListeners("event");
+
+customEmitterObj.emit("event");
+customEmitterObj.emit("event", { /* event object */ });
+
+customEmitterObj.eventNames();  // string[] of the events it listens to
+customEmitterObj.listenerCount("event");  // num of listeners for an event
+customEmitterObj.listeners();  // Function[], handlers of the events
+```