More cleanly support isConnected usage with a bool return value

Related to discussion on #1015

README.md

@@ -838,9 +838,14 @@ Function `stopNotification` stops a previously registered notification callback.
 Reports the connection status.
 
 ```javascript
+// Callbacks
 ble.isConnected(device_id, success, failure);
-// Or using await with promises
-await ble.withPromises.isConnected(device_id);
+
+// Promises with boolean return
+const isConnected = await ble.withPromises.isConnected(device_id, false);
+
+// Promises with rejection
+await ble.withPromises.isConnected(device_id); // throws if not connected
 ```
 
 ### Description
@@ -858,6 +863,7 @@ NOTE that for many apps isConnected is unncessary. The app can track the connect
 ### Quick Example
 
 ```javascript
+// Callbacks
 ble.isConnected(
     'FFCA0B09-CB1D-4DC0-A1EF-31AFD3EDFB53',
     function () {
@@ -867,6 +873,22 @@ ble.isConnected(
         console.log('Peripheral is *not* connected');
     }
 );
+
+// Promises with boolean return
+const isConnected = await ble.withPromises.isConnected(device_id, false);
+if (isConnected) {
+    console.log('Peripheral is connected');
+} else {
+    console.log('Peripheral is *not* connected');
+}
+
+// Promises with rejection
+try {
+    await ble.withPromises.isConnected(device_id);
+    console.log('Peripheral is connected');
+} catch (e) {
+    console.log('Peripheral is *not* connected');
+}
 ```
 
 ## isEnabled

types.d.ts

@@ -160,9 +160,14 @@ declare namespace BLECentralPlugin {
         ): Promise<void>;
         stopNotification(device_id: string, service_uuid: string, characteristic_uuid: string): Promise<void>;
 
-        /* Returns a rejected promise if the device is not connected */
+        /* Returns a resolved promise if the device is connected,
+            otherwise returns rejected promise if the device is not connected */
         isConnected(device_id: string): Promise<void>;
 
+        /* Returns a promise that resolves to true if the device is connected,
+            otherwise resolves to false if the device is not connected or an error occurs */
+        isConnected(device_id: string, rejectWhenDisconnected: false): Promise<boolean>;
+
         /* Returns a rejected promise if bluetooth is not connected */
         isEnabled(): Promise<void>;
 

www/ble.js

@@ -362,9 +362,17 @@ module.exports.withPromises = {
         });
     },
 
-    isConnected: function (device_id) {
+    isConnected: function (device_id, rejectWhenDisconnected) {
         return new Promise(function (resolve, reject) {
-            module.exports.isConnected(device_id, resolve, reject);
+            if (rejectWhenDisconnected === false) {
+                module.exports.isConnected(
+                    device_id,
+                    () => resolve(true),
+                    () => resolve(false)
+                );
+            } else {
+                module.exports.isConnected(device_id, resolve, reject);
+            }
         });
     },