doc: general improvments to events documentation

PR-URL: https://github.com/nodejs/node/pull/7480
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/events.md

@@ -15,11 +15,11 @@ a [stream][] emits an event whenever data is available to be read.
 
 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,
+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
+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 will be discarded.
 
@@ -109,7 +109,8 @@ myEmitter.emit('event');
 ```
 
 Using the `eventEmitter.once()` method, it is possible to register a listener
-that is unregistered before it is called.
+that is called at most once for a particular event. Once the event is emitted,
+the listener is unregistered and *then* called.
 
 ```js
 const myEmitter = new MyEmitter();
@@ -126,7 +127,7 @@ myEmitter.emit('event');
 ## Error events
 
 When an error occurs within an `EventEmitter` instance, the typical action is
-for an `'error'` event to be emitted. These are treated as a special case
+for an `'error'` event to be emitted. These are treated as special cases
 within Node.js.
 
 If an `EventEmitter` does _not_ have at least one listener registered for the
@@ -139,10 +140,9 @@ myEmitter.emit('error', new Error('whoops!'));
   // Throws and crashes Node.js
 ```
 
-To guard against crashing the Node.js process, developers can either register
-a listener for the `process.on('uncaughtException')` event or use the
-[`domain`][] module (_Note, however, that the `domain` module has been
-deprecated_).
+To guard against crashing the Node.js process, a listener can be registered
+on the [`process` object's `uncaughtException` event][] or the [`domain`][] module
+can be used. (_Note, however, that the `domain` module has been deprecated_)
 
 ```js
 const myEmitter = new MyEmitter();
@@ -155,8 +155,7 @@ myEmitter.emit('error', new Error('whoops!'));
   // Prints: whoops! there was an error
 ```
 
-As a best practice, developers should always register listeners for the
-`'error'` event:
+As a best practice, listeners should always be added for the `'error'` events.
 
 ```js
 const myEmitter = new MyEmitter();
@@ -176,15 +175,15 @@ const EventEmitter = require('events');
 ```
 
 All EventEmitters emit the event `'newListener'` when new listeners are
-added and `'removeListener'` when a listener is removed.
+added and `'removeListener'` when existing listeners are removed.
 
 ### Event: 'newListener'
 
 * `eventName` {String|Symbol} The name of the event being listened for
 * `listener` {Function} The event handler function
 
-The `EventEmitter` instance will emit it's own `'newListener'` event *before*
-a listener is added to it's internal array of listeners.
+The `EventEmitter` instance will emit its own `'newListener'` event *before*
+a listener is added to its internal array of listeners.
 
 Listeners registered for the `'newListener'` event will be passed the event
 name and a reference to the listener being added.
@@ -219,7 +218,7 @@ myEmitter.emit('event');
 * `eventName` {String|Symbol} The event name
 * `listener` {Function} The event handler function
 
-The `'removeListener'` event is emitted *after* a listener is removed.
+The `'removeListener'` event is emitted *after* the `listener` is removed.
 
 ### EventEmitter.listenerCount(emitter, eventName)
 
@@ -251,7 +250,7 @@ precedence over `EventEmitter.defaultMaxListeners`.
 
 Note that this is not a hard limit. The `EventEmitter` instance will allow
 more listeners to be added but will output a trace warning to stderr indicating
-that a `possible EventEmitter memory leak` has been detected. For any single
+that a "possible EventEmitter memory leak" has been detected. For any single
 `EventEmitter`, the `emitter.getMaxListeners()` and `emitter.setMaxListeners()`
 methods can be used to temporarily avoid this warning:
 
@@ -301,7 +300,7 @@ set by [`emitter.setMaxListeners(n)`][] or defaults to
 
 ### emitter.listenerCount(eventName)
 
-* `eventName` {Value} The name of the event being listened for
+* `eventName` {String|Symbol} The name of the event being listened for
 
 Returns the number of listeners listening to the event named `eventName`.
 
@@ -319,7 +318,7 @@ console.log(util.inspect(server.listeners('connection')));
 
 ### emitter.on(eventName, listener)
 
-* `eventName` {string|Symbol} The name of the event.
+* `eventName` {String|Symbol} The name of the event.
 * `listener` {Function} The callback function
 
 Adds the `listener` function to the end of the listeners array for the
@@ -334,7 +333,7 @@ server.on('connection', (stream) => {
 });
 ```
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 By default, event listeners are invoked in the order they are added. The
 `emitter.prependListener()` method can be used as an alternative to add the
@@ -352,7 +351,7 @@ myEE.emit('foo');
 
 ### emitter.once(eventName, listener)
 
-* `eventName` {string|Symbol} The name of the event.
+* `eventName` {String|Symbol} The name of the event.
 * `listener` {Function} The callback function
 
 Adds a **one time** `listener` function for the event named `eventName`. The
@@ -364,7 +363,7 @@ server.once('connection', (stream) => {
 });
 ```
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 By default, event listeners are invoked in the order they are added. The
 `emitter.prependOnceListener()` method can be used as an alternative to add the
@@ -382,7 +381,7 @@ myEE.emit('foo');
 
 ### emitter.prependListener(eventName, listener)
 
-* `eventName` {string|Symbol} The name of the event.
+* `eventName` {String|Symbol} The name of the event.
 * `listener` {Function} The callback function
 
 Adds the `listener` function to the *beginning* of the listeners array for the
@@ -397,11 +396,11 @@ server.prependListener('connection', (stream) => {
 });
 ```
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 ### emitter.prependOnceListener(eventName, listener)
 
-* `eventName` {string|Symbol} The name of the event.
+* `eventName` {String|Symbol} The name of the event.
 * `listener` {Function} The callback function
 
 Adds a **one time** `listener` function for the event named `eventName` to the
@@ -414,7 +413,7 @@ server.prependOnceListener('connection', (stream) => {
 });
 ```
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 ### emitter.removeAllListeners([eventName])
 
@@ -424,7 +423,7 @@ Note that it is bad practice to remove listeners added elsewhere in the code,
 particularly when the `EventEmitter` instance was created by some other
 component or module (e.g. sockets or file streams).
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 ### emitter.removeListener(eventName, listener)
 
@@ -485,10 +484,10 @@ myEmitter.emit('event');
 Because listeners are managed using an internal array, calling this will
 change the position indices of any listener registered *after* the listener
 being removed. This will not impact the order in which listeners are called,
-but it will means that any copies of the listener array as returned by
+but it means that any copies of the listener array as returned by
 the `emitter.listeners()` method will need to be recreated.
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 ### emitter.setMaxListeners(n)
 
@@ -499,7 +498,7 @@ The `emitter.setMaxListeners()` method allows the limit to be modified for this
 specific `EventEmitter` instance. The value can be set to `Infinity` (or `0`)
 to indicate an unlimited number of listeners.
 
-Returns a reference to the `EventEmitter` so calls can be chained.
+Returns a reference to the `EventEmitter`, so that calls can be chained.
 
 [`net.Server`]: net.html#net_class_net_server
 [`fs.ReadStream`]: fs.html#fs_class_fs_readstream
@@ -507,4 +506,5 @@ Returns a reference to the `EventEmitter` so calls can be chained.
 [`EventEmitter.defaultMaxListeners`]: #events_eventemitter_defaultmaxlisteners
 [`emitter.listenerCount()`]: #events_emitter_listenercount_eventname
 [`domain`]: domain.html
+[`process` object's `uncaughtException` event]: process.html#process_event_uncaughtexception
 [stream]: stream.html