Add support for sessionId to events too

Allow to filter events by `sessionId`. There is one gotcha that when
using promises without filter, the `sessionId` is not returned due to
the limitation of promises to return only one value, and the fact that
changing the return type would be a breaking change.

Related to #441.

README.md

@@ -689,7 +689,8 @@ Emitted when the remote instance sends any notification through the WebSocket.
 
 - `method`: a string describing the notification (e.g.,
   `'Network.requestWillBeSent'`);
-- `params`: an object containing the payload.
+- `params`: an object containing the payload;
+- `sessionId`: an optional string representing the session identifier.
 
 Refer to the [Chrome Debugging Protocol] specification for more information.
 
@@ -706,14 +707,16 @@ client.on('event', (message) => {
 #### Event: '`<domain>`.`<method>`'
 
 ```js
-function (params) {}
+function (params, sessionId) {}
 ```
 
 Emitted when the remote instance sends a notification for `<domain>.<method>`
 through the WebSocket.
 
 `params` is an object containing the payload.
 
+`sessionId` is an optional string representing the session identifier.
+
 This is just a utility event which allows to easily listen for specific
 notifications (see [`'event'`](#event-event)), for example:
 
@@ -727,6 +730,18 @@ Additionally, the equivalent `<domain>.on('<method>', ...)` syntax is available,
 client.Network.on('requestWillBeSent', console.log);
 ```
 
+#### Event: '`<domain>`.`<method>`.`<sessionId>`'
+
+```js
+function (params, sessionId) {}
+```
+
+Equivalent to the following but only for those events belonging to the given `session`:
+
+```js
+client.on('<domain>.<event>', callback);
+```
+
 #### Event: 'ready'
 
 ```js
@@ -819,16 +834,16 @@ For example:
 client.Page.navigate({url: 'https://github.com'}, console.log);
 ```
 
-#### client.`<domain>`.`<event>`([callback])
+#### client.`<domain>`.`<event>`([sessionId], [callback])
 
 Just a shorthand for:
 
 ```js
-client.on('<domain>.<event>', callback);
+client.on('<domain>.<event>[.<sessionId>]', callback);
 ```
 
 When `callback` is omitted the event is registered only once and a `Promise`
-object is returned.
+object is returned. Notice though that in this case the optional `sessionId` usually passed to `callback` is not returned.
 
 When `callback` is provided, it returns a function that can be used to
 unsubscribe `callback` from the event, it can be useful when anonymous functions
@@ -837,7 +852,7 @@ are used as callbacks.
 For example:
 
 ```js
-const unsubscribe = client.Network.requestWillBeSent((params) => {
+const unsubscribe = client.Network.requestWillBeSent((params, sessionId) => {
     console.log(params.request.url);
 });
 unsubscribe();

lib/api.js

@@ -37,13 +37,18 @@ function addCommand(chrome, domainName, command) {
 
 function addEvent(chrome, domainName, event) {
     const eventName = `${domainName}.${event.name}`;
-    const handler = (handler) => {
+    const handler = (sessionId, handler) => {
+        if (typeof sessionId === 'function') {
+            handler = sessionId;
+            sessionId = undefined;
+        }
+        const rawEventName = sessionId ? `${eventName}.${sessionId}` : eventName;
         if (typeof handler === 'function') {
-            chrome.on(eventName, handler);
-            return () => chrome.removeListener(eventName, handler);
+            chrome.on(rawEventName, handler);
+            return () => chrome.removeListener(rawEventName, handler);
         } else {
             return new Promise((fulfill, reject) => {
-                chrome.once(eventName, fulfill);
+                chrome.once(rawEventName, fulfill);
             });
         }
     };

lib/chrome.js

@@ -267,8 +267,10 @@ class Chrome extends EventEmitter {
         }
         // event
         else if (message.method) {
+            const {method, params, sessionId} = message;
             this.emit('event', message);
-            this.emit(message.method, message.params);
+            this.emit(method, params, sessionId);
+            this.emit(`${method}.${sessionId}`, params, sessionId);
         }
     }
 

test/event.js

@@ -92,4 +92,45 @@ describe('registering event', () => {
             });
         });
     });
+    describe('passing a sessionId', () => {
+        it('should only listen for those events', async () => {
+            // fetch and connect to the browser target
+            const version = await Chrome.Version();
+            const chrome = await Chrome({
+                target: version.webSocketDebuggerUrl
+            });
+            // create another target
+            await chrome.Target.createTarget({url: 'about:blank'});
+            // fetch the targets (two pages) and attach to each of them
+            const {targetInfos} = await chrome.Target.getTargets();
+            const {sessionId: sessionId0} = await chrome.Target.attachToTarget({
+                targetId: targetInfos[0].targetId,
+                flatten: true
+            });
+            const {sessionId: sessionId1} = await chrome.Target.attachToTarget({
+                targetId: targetInfos[1].targetId,
+                flatten: true
+            });
+            // enable the Page events in both of them
+            await chrome.Page.enable(sessionId0);
+            await chrome.Page.enable(sessionId1);
+            // trigger a reload in both of them
+            chrome.Page.reload(sessionId0);
+            chrome.Page.reload(sessionId1);
+            // awaits individual events
+            await Promise.all([
+                chrome.Page.loadEventFired(sessionId0),
+                chrome.Page.loadEventFired(sessionId1),
+                new Promise((fulfill, reject) => {
+                    let counter = 0;
+                    chrome.Page.loadEventFired((params) => {
+                        if (++counter == 2) {
+                            fulfill();
+                        }
+                    });
+                })
+            ]);
+            return chrome.close();
+        });
+    });
 });