fix: Don't interpret string values as relative if they do not start w…

…ith a sign. Closes #239 and also add tests to define the behaviour of relative values, closes #243

examples/09_relative_values.html

@@ -28,11 +28,13 @@
 			function init() {
 				var target1 = document.getElementById( 'target1' ),
 					tween1 = new TWEEN.Tween( target1.dataset )
-						.to( { top: "+20", left: "-20" }, 1000 )
+						.to( { top: "+20", left: "-20" }, 500 )
 						.repeat( 5 )
 						.delay( 500 )
 						.easing( TWEEN.Easing.Exponential.In )
 						.onUpdate( function() {
+							this.top = Math.round(this.top);
+							this.left = Math.round(this.left);
 							updateBox( target1, this );
 						})
 						.start();
@@ -43,17 +45,14 @@
 			function animate( time ) {
 
 				requestAnimationFrame( animate );
-
 				TWEEN.update( time );
 
 			}
 
 			function updateBox( box, params ) {
-				var field,
-					s = box.style;
-				for (field in params) {
-					s[field] = params[field] + "px";
-				}
+				var s = box.style;
+				var transform = 'translate(' + params.left + 'px, ' + params.top + 'px)';
+				s.transform = transform;
 			}
 
 		</script>
@@ -65,7 +64,7 @@ <h2>09 _ relative values</h2>
 			<p>Tweening to relative values, with repeat.</p>
 		</div>
 		<div style="position: absolute; left: 400px; ">
-			<div id="target1" style="position: absolute;" data-top="150" class="box">
+			<div id="target1" style="position: absolute;" data-top="150" data-left="150" class="box">
 			</div>
 		</div>
 	</body>

src/Tween.js

@@ -315,7 +315,12 @@ TWEEN.Tween = function (object) {
 
 				// Parses relative end values with start as base (e.g.: +10, -3)
 				if (typeof (end) === 'string') {
-					end = start + parseFloat(end, 10);
+
+					if (end.startsWith('+') || end.startsWith('-')) {
+						end = start + parseFloat(end, 10);
+					} else {
+						end = parseFloat(end, 10);
+					}
 				}
 
 				// Protect against non numeric properties.

test/unit/tests.js

@@ -286,6 +286,48 @@
 
 			},
 
+			'Tween relative positive value, with sign': function(test) {
+
+				var obj = { x: 0 },
+					t = new TWEEN.Tween( obj );
+
+				t.to( { x: "+100" }, 1000 );
+				t.start( 0 );
+				t.update( 1000 );
+
+				test.equal( obj.x, 100 );
+				test.done();
+
+			},
+
+			'Tween relative negative value': function(test) {
+
+				var obj = { x: 0 },
+					t = new TWEEN.Tween( obj );
+
+				t.to( { x: "-100" }, 1000 );
+				t.start( 0 );
+				t.update( 1000 );
+
+				test.equal( obj.x, -100 );
+				test.done();
+
+			},
+
+			'String values without a + or - sign should not be interpreted as relative': function(test) {
+
+				var obj = { x: 100 },
+					t = new TWEEN.Tween( obj );
+
+				t.to( { x: "100" }, 1000 );
+				t.start( 0 );
+				t.update( 1000 );
+
+				test.equal( obj.x, 100 );
+				test.done();
+
+			},
+
 			'Test TWEEN.Tween.start()': function(test) {
 
 				var obj = { },