Add #hasEnded() (#151)

* Add #hasEnded()

Co-authored-by: Jeremy Kahn <jeremyckahn@gmail.com>

src/tweenable.js

@@ -130,11 +130,11 @@ const processTween = (tween, currentTime) => {
 
   const endTime = timestamp + delay + duration
   let timeToCompute = currentTime > endTime ? endTime : currentTime
-  const hasEnded = timeToCompute >= endTime
+  tween._hasEnded = timeToCompute >= endTime
   const offset = duration - (endTime - timeToCompute)
   const hasFilters = tween._filters.length > 0
 
-  if (hasEnded) {
+  if (tween._hasEnded) {
     tween._render(targetState, tween._data, offset)
     return tween.stop(true)
   }
@@ -321,6 +321,8 @@ export class Tweenable {
     /** @private */
     this._timestamp = null
     /** @private */
+    this._hasEnded = false
+    /** @private */
     this._resolve = null
     /** @private */
     this._reject = null
@@ -717,6 +719,15 @@ export class Tweenable {
     return this._isPlaying
   }
 
+  /**
+   * Whether or not a tween has finished running.
+   * @method Tweenable#hasEnded
+   * @return {boolean}
+   */
+  hasEnded() {
+    return this._hasEnded
+  }
+
   /**
    * @method Tweenable#setScheduleFunction
    * @param {shifty.scheduleFunction} scheduleFunction

src/tweenable.test.js

@@ -324,6 +324,37 @@ describe('#tween', () => {
   })
 })
 
+describe('#hasEnded', () => {
+  test('Only trigger after the end of the tween', () => {
+    tweenable = new Tweenable()
+
+    tweenable.tween({
+      from: { x: 0 },
+      to: { x: 10 },
+      duration: 500,
+    })
+
+    expect(tweenable.hasEnded()).toBe(false)
+    tweenable.seek(500)
+    expect(tweenable.hasEnded()).toBe(true)
+  })
+
+  test('Triggers again after restarting the tween', () => {
+    tweenable = new Tweenable()
+
+    tweenable.tween({
+      from: { x: 0 },
+      to: { x: 10 },
+      duration: 500,
+    })
+
+    tweenable.seek(500)
+    expect(tweenable.hasEnded()).toBe(true)
+    tweenable.seek(0)
+    expect(tweenable.hasEnded()).toBe(false)
+  })
+})
+
 describe('#resume', () => {
   beforeEach(() => {
     Tweenable.now = () => 0