add Map#isZooming method (#6128)

* add Map#isZooming method

* initialize Camera#zooming

src/ui/camera.js

@@ -83,6 +83,7 @@ class Camera extends Evented {
     constructor(transform: Transform, options: {bearingSnap: number}) {
         super();
         this.moving = false;
+        this.zooming = false;
         this.transform = transform;
         this._bearingSnap = options.bearingSnap;
     }
@@ -858,6 +859,16 @@ class Camera extends Evented {
         return this.moving;
     }
 
+    /**
+     * Returns a Boolean indicating whether the camera is zooming.
+     *
+     * @memberof Map#
+     * @returns A Boolean indicating whether the camera is zooming.
+     */
+    isZooming(): boolean {
+        return this.zooming;
+    }
+
     /**
      * Stops any animated transition underway.
      *

test/unit/ui/map.test.js

@@ -1268,6 +1268,23 @@ test('Map', (t) => {
         map.zoomTo(5, { duration: 0 });
     });
 
+    t.test('Map#isZooming', (t) => {
+        t.plan(3);
+        const map = createMap();
+
+        t.equal(map.isZooming(), false, 'false before zooming');
+
+        map.on('zoomstart', () => {
+            t.equal(map.isZooming(), true, 'true on zoomstart');
+        });
+
+        map.on('zoomend', () => {
+            t.equal(map.isZooming(), false, 'false on zoomend');
+        });
+
+        map.zoomTo(5, { duration: 0 });
+    });
+
     t.end();
 });