feat(UIEventObserver): add UIEventObserver#subscribeOnce

azu · Nov 25, 2016 · 4dfe592 · 4dfe592
1 parent 20202c8
commit 4dfe592
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Showing 2 changed files with 57 additions and 0 deletions.
diff --git a/src/UIEventObserver.js b/src/UIEventObserver.js
@@ -17,6 +17,7 @@ export default class UIEventObserver {
      * @param {Object} target target Element Node
      * @param {string} eventName event name
      * @param {Function} handler event handler
+     * @returns {Function} unsubscribe handler
      * @public
      */
     subscribe(target, eventName, handler) {
@@ -31,6 +32,26 @@ export default class UIEventObserver {
             target.addEventListener(eventName, handler);
         }
         domEventEmitter.on(handler);
+        return () => {
+            this.unsubscribe(target, eventName, handler);
+        }
+    }
+
+    /**
+     * registers the specified `handler` on the `target` element it's called `eventName`.
+     * It is called at once difference from UIEventObserver#subscribe
+     * @param {Object} target target Element Node
+     * @param {string} eventName event name
+     * @param {Function} handler event handler
+     * @returns {Function} unsubscribe handler
+     * @public
+     */
+    subscribeOnce(target, eventName, handler) {
+        const onceHandler = (event) => {
+            handler(event);
+            this.unsubscribe(target, eventName, onceHandler);
+        };
+        return this.subscribe(target, eventName, onceHandler);
     }
 
     /**

diff --git a/test/UIEventObserver-test.js b/test/UIEventObserver-test.js
@@ -12,6 +12,23 @@ describe("UIEventObserver", () => {
         eventObserver.unsubscribeAll();
     });
     describe("#subscribe", () => {
+        context("return values", () => {
+            it("is unsubscribe function bind arguments", () => {
+                const called = [];
+                const handler = (event) => {
+                    called.push(event);
+                };
+                const unsubscribe = eventObserver.subscribe(window, "scroll", handler);
+                assert(typeof unsubscribe === "function");
+                assert(called.length === 0);
+                // unsubscribe
+                unsubscribe();
+                // fire
+                const event = new Event("scroll");
+                window.dispatchEvent(event);
+                assert(called.length === 0);
+            });
+        });
         context("target is document.body", () => {
             it("add handler is called when the event is fired", (done) => {
                 const handler = (event) => {
@@ -52,6 +69,25 @@ describe("UIEventObserver", () => {
             });
         });
     });
+    describe("#subscribeOnce", () => {
+        context("when fire it once", () => {
+            it("should automatically unsubscribe", () => {
+                const called = [];
+                const handler = (event) => {
+                    called.push(event);
+                };
+                const unsubscribe = eventObserver.subscribeOnce(window, "scroll", handler);
+                assert(typeof unsubscribe === "function");
+                assert(called.length === 0);
+                // fire
+                window.dispatchEvent(new Event("scroll"));
+                assert(called.length === 1);
+                // fire twice, but is not called
+                window.dispatchEvent(new Event("scroll"));
+                assert(called.length === 1);
+            });
+        });
+    });
     describe("#unsubscribe", () => {
         it("unSubscribe all -> Actual removeEventListener", () => {
             const handler = () => {