fix(property): add missing support for observe method

Author: smalluban

Diff for: docs/core-features/property.md

@@ -9,12 +9,13 @@ Property factory provides the most basic feature - it holds the property value.
 ## Usage
 
 ```typescript
-property(defaultValue: any, [connect: Function]): Object
+property(defaultValue: any, connect: Function, observe: Function): Object
 ```
 
 * **arguments**:
   * `defaultValue` - any value
   * `connect` - a connect callback function of the property descriptor
+  * `observe` - an observe callback function of the property descriptor
 * **returns**:
   * a property descriptor, which resolves to value
 

Diff for: docs/misc/api-reference.md

@@ -27,12 +27,13 @@ define({ tagName: descriptors, ... }): { tagName: Wrapper, ... }
 ## property
 
 ```typescript
-property(defaultValue: any, [connect: Function]): Object
+property(defaultValue: any, connect: Function, observe: Function): Object
 ```
 
 * **arguments**:
   * `defaultValue` - any value
   * `connect` - a connect callback function of the property descriptor
+  * `observe` - an observe callback function of the property descriptor
 * **returns**:
   * a property descriptor, which resolves to value
 

Diff for: src/property.js

@@ -9,7 +9,7 @@ const objectTransform = value => {
   return value && Object.freeze(value);
 };
 
-export default function property(value, connect) {
+export default function property(value, connect, observe) {
   const attrs = new WeakMap();
   const type = typeof value;
   let transform = defaultTransform;
@@ -38,7 +38,7 @@ export default function property(value, connect) {
 
   return {
     get: (host, val = value) => val,
-    set: (host, val, oldValue = value) => transform(val, oldValue),
+    set: (host, val, lastValue = value) => transform(val, lastValue),
     connect:
       type !== "object" && type !== "undefined"
         ? (host, key, invalidate) => {
@@ -57,21 +57,23 @@ export default function property(value, connect) {
           }
         : connect,
     observe:
-      type !== "object" &&
-      type !== "undefined" &&
-      ((host, val) => {
-        const attrName = attrs.get(host);
+      type !== "object" && type !== "undefined"
+        ? (host, val, lastValue) => {
+            const attrName = attrs.get(host);
+
+            const attrValue = host.getAttribute(attrName);
+            const nextValue = val === true ? "" : val;
 
-        const attrValue = host.getAttribute(attrName);
-        const nextValue = val === true ? "" : val;
+            if (nextValue === attrValue) return;
 
-        if (nextValue === attrValue) return;
+            if (val !== 0 && !val) {
+              host.removeAttribute(attrName);
+            } else {
+              host.setAttribute(attrName, nextValue);
+            }
 
-        if (val !== 0 && !val) {
-          host.removeAttribute(attrName);
-        } else {
-          host.setAttribute(attrName, nextValue);
-        }
-      }),
+            if (observe) observe(host, val, lastValue);
+          }
+        : observe,
   };
 }

Diff for: test/spec/property.js

@@ -286,4 +286,32 @@ describe("property:", () => {
       )(done);
     });
   });
+
+  describe("observe option", () => {
+    it("is called for primitive default value", done => {
+      const spy = jasmine.createSpy("observe");
+      define("test-property-connect", {
+        prop: property(0, null, spy),
+      });
+
+      test("<test-property-connect></test-property-connect>")(() =>
+        resolveRaf(() => {
+          expect(spy).toHaveBeenCalledTimes(1);
+        }),
+      )(done);
+    });
+
+    it("is called for object default value", done => {
+      const spy = jasmine.createSpy("observe");
+      define("test-property-connect", {
+        prop: property({}, null, spy),
+      });
+
+      test("<test-property-connect></test-property-connect>")(() =>
+        resolveRaf(() => {
+          expect(spy).toHaveBeenCalledTimes(1);
+        }),
+      )(done);
+    });
+  });
 });

Diff for: types/index.d.ts

@@ -1,4 +1,4 @@
-declare module 'hybrids' {
+declare module "hybrids" {
   interface InvalidateOptions {
     force?: boolean;
   }
@@ -77,6 +77,7 @@ declare module 'hybrids' {
   function property<E, V>(
     value: V | null | undefined | ((value: any) => V),
     connect?: Descriptor<E, V>["connect"],
+    observe?: Descriptor<E, V>["observe"],
   ): Descriptor<E, V>;
 
   function parent<E, V>(