add interval to clock

src/mocks/Clock.js

@@ -18,6 +18,34 @@ class Timeout {
     }
 }
 
+class Interval {
+    constructor(elapsed, ms, callback) {
+        this._start = elapsed.get();
+        this._last = this._start;
+        this._interval = ms;
+        this._callback = callback;
+        this._subscription = elapsed.subscribe(this._update.bind(this));
+    }
+
+    _update(elapsed) {
+        const prevAmount = Math.floor((this._last - this._start) / this._interval);
+        const newAmount = Math.floor((elapsed - this._start) / this._interval);
+        const amountDiff = Math.max(0, newAmount - prevAmount);
+        this._last = elapsed;
+
+        for (let i = 0; i < amountDiff; ++i) {
+            this._callback();
+        }
+    }
+
+    dispose() {
+        if (this._subscription) {
+            this._subscription();
+            this._subscription = null;
+        }
+    }
+}
+
 class TimeMeasure {
     constructor(elapsed) {
         this._elapsed = elapsed;
@@ -47,6 +75,10 @@ export class Clock {
         return new Timeout(this._elapsed, ms);
     }
 
+    createInterval(callback, ms) {
+        return new Interval(this._elapsed, ms, callback);
+    }
+
     now() {
         return this._baseTimestamp + this.elapsed;
     }
@@ -72,6 +104,16 @@ export function tests() {
             const promise = timeout.elapsed();
             assert(promise instanceof Promise);
             await promise;
+        },
+        "test interval": assert => {
+            const clock = new Clock();
+            let counter = 0;
+            const interval = clock.createInterval(() => counter += 1, 200);
+            clock.elapse(150);
+            assert.strictEqual(counter, 0);
+            clock.elapse(500);
+            assert.strictEqual(counter, 3);
+            interval.dispose();
         }
     }
 }

src/ui/web/dom/Clock.js

@@ -25,8 +25,26 @@ class Timeout {
             this._reject = null;
         }
     }
+
+    dispose() {
+        this.abort();
+    }
 }
 
+class Interval {
+    constructor(ms, callback) {
+        this._handle = setInterval(callback, ms);
+    }
+
+    dispose() {
+        if (this._handle) {
+            clearInterval(this._handle);
+            this._handle = null;
+        }
+    }
+}
+
+
 class TimeMeasure {
     constructor() {
         this._start = window.performance.now();
@@ -46,6 +64,10 @@ export class Clock {
         return new Timeout(ms);
     }
 
+    createInterval(callback, ms) {
+        return new Interval(ms, callback);
+    }
+
     now() {
         return Date.now();
     }