Allow silent changes to observed property

js/src/observe.js

@@ -30,6 +30,9 @@ export default class uObserve {
    * @param {ObserveCallback=} p2
    */
   static observe(obj, p1, p2) {
+    if (typeof obj !== 'object' || obj === null) {
+      throw new Error('Invalid argument: invalid object');
+    }
     if (typeof p2 === 'function') {
       this.observeProperty(obj, p1, p2);
     } else if (typeof p1 === 'function') {
@@ -62,6 +65,31 @@ export default class uObserve {
     }
   }
 
+  static isObserved(obj, property) {
+    if (typeof obj !== 'object' || obj === null) {
+      return false;
+    }
+    return obj.hasOwnProperty(property) && obj.hasOwnProperty('_values') &&
+      obj._values.hasOwnProperty(property) && !!Object.getOwnPropertyDescriptor(obj, property)['set'];
+  }
+
+  /**
+   * Set observed property value without notifying observers
+   * @param {Object} obj
+   * @param {string} property
+   * @param {*} value
+   */
+  static setSilently(obj, property, value) {
+    if (!obj.hasOwnProperty(property)) {
+      throw new Error(`Invalid argument: object does not have property "${property}"`);
+    }
+    if (this.isObserved(obj, property)) {
+      obj._values[property] = value;
+    } else {
+      obj[property] = value;
+    }
+  }
+
   /**
    * Observe object's property. On change call observer
    * @param {Object} obj
@@ -69,6 +97,9 @@ export default class uObserve {
    * @param {ObserveCallback} observer
    */
   static observeProperty(obj, property, observer) {
+    if (!obj.hasOwnProperty(property)) {
+      throw new Error(`Invalid argument: object does not have property "${property}"`);
+    }
     this.addObserver(obj, observer, property);
     if (!obj.hasOwnProperty('_values')) {
       Object.defineProperty(obj, '_values', { enumerable: false, configurable: false, value: {} });

js/test/observe.test.js

@@ -334,6 +334,65 @@ describe('Observe tests', () => {
       expect(resultValue2).toEqual(undefined);// eslint-disable-line no-undefined
       expect(array).toEqual([ 1, 2, 3 ]);
     });
+
+    it('should throw error when observing non-existing property', () => {
+      // given
+      const nonExisting = '___non-existing___';
+
+      expect(object.hasOwnProperty(nonExisting)).toBe(false);
+      // then
+      expect(() => uObserve.observe(object, nonExisting, (value) => {
+        result = true;
+        resultValue = value;
+      })).toThrow();
+
+      expect(object.hasOwnProperty(nonExisting)).toBe(false);
+    });
+
+    it('should throw error when observing non-object', () => {
+      // given
+      const nonExisting = '___non-existing___';
+      // then
+      expect(() => uObserve.observe(nonExisting, (value) => {
+        result = true;
+        resultValue = value;
+      })).toThrow();
+    });
+
+    it('should throw error when observing null object', () => {
+      // given
+      const nullObject = null;
+      // then
+      expect(() => uObserve.observe(nullObject, (value) => {
+        result = true;
+        resultValue = value;
+      })).toThrow();
+    });
+
+    it('should not notify observers when observed property is silently changed', () => {
+      // given
+      uObserve.observe(object, 'observed', (value) => {
+        result = true;
+        resultValue = value;
+      });
+      // when
+      expect(result).toBe(false);
+      uObserve.setSilently(object, 'observed', 2);
+      // then
+      expect(result).toBe(false);
+      // eslint-disable-next-line no-undefined
+      expect(resultValue).toBe(undefined);
+    });
+
+    it('should return true if property is observed', () => {
+      // when
+      uObserve.observe(object, 'observed', (value) => {
+        result = true;
+        resultValue = value;
+      });
+      // then
+      expect(uObserve.isObserved(object, 'observed')).toBe(true);
+    });
   });
 
   describe('when notify is called directly', () => {
@@ -351,5 +410,6 @@ describe('Observe tests', () => {
       expect(result).toBe(true);
       expect(result2).toBe(true);
     });
+
   });
 });