Multiple .start() and .to(prop:[])

src/Tween.ts

@@ -44,6 +44,7 @@ export class Tween<T extends UnknownProps> {
 	private _onStopCallback?: (object: T) => void
 	private _id = Sequence.nextId()
 	private _isChainStopped = false
+	private _hasSetupProperty = false
 
 	constructor(private _object: T, private _group: Group | false = mainGroup) {}
 
@@ -65,6 +66,7 @@ export class Tween<T extends UnknownProps> {
 		// currently no opt-out).
 		// for (const prop in properties) this._valuesEnd[prop] = properties[prop]
 		this._valuesEnd = Object.create(properties)
+		this._hasSetupProperty = false
 
 		if (duration !== undefined) {
 			this._duration = duration
@@ -146,7 +148,9 @@ export class Tween<T extends UnknownProps> {
 				endValues = endValues.map(this._handleRelativeValue.bind(this, startValue as number))
 
 				// Create a local copy of the Array with the start value at the front
-				_valuesEnd[property] = [startValue].concat(endValues)
+				if (!this._hasSetupProperty) {
+					_valuesEnd[property] = [_valuesStart[property] ?? startValue].concat(endValues)
+				}
 			}
 
 			// handle the deepness of the values
@@ -186,6 +190,7 @@ export class Tween<T extends UnknownProps> {
 				}
 			}
 		}
+		this._hasSetupProperty = true
 	}
 
 	stop(): this {

src/tests.ts

@@ -1919,6 +1919,52 @@ export const tests = {
 		test.done()
 	},
 
+	'Tween.to(value:[number]) and Tween.to(value:number) return the same result after multiple .start()'(
+		test: Test,
+	): void {
+		const toNumber = {x: 1.0}
+		const toArray = {x: [1.0]}
+		const targetNumber = {x: 0.0}
+		const targetArray = {x: 0.0}
+		const tweenNumber = new TWEEN.Tween(targetNumber).to(toNumber, 100)
+		const tweenArray = new TWEEN.Tween(targetArray).to(toArray, 100)
+
+		tweenNumber.start(0)
+		tweenArray.start(0)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(37)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(50)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(100)
+		test.equal(targetNumber.x, targetArray.x)
+
+		tweenNumber.start(100)
+		tweenArray.start(100)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(137)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(150)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(200)
+		test.equal(targetNumber.x, targetArray.x)
+
+		//should keep _valuesStart after .to() function
+		tweenNumber.to({x: 2.0})
+		tweenArray.to({x: [2.0]})
+		tweenNumber.start(200)
+		tweenArray.start(200)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(237)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(250)
+		test.equal(targetNumber.x, targetArray.x)
+		TWEEN.update(300)
+		test.equal(targetNumber.x, targetArray.x)
+
+		test.done()
+	},
+
 	'Test TWEEN.Tween.update() with no arguments'(test: Test): void {
 		const clock = FakeTimers.install()
 		const targetNow = {x: 0.0}