.css(), the values like +=10% aren't ignored anymore (like .animate())

src/css.js

@@ -1,13 +1,15 @@
 define([
 	"./core",
 	"./var/pnum",
+	"./var/rfxnum",
 	"./core/access",
 	"./css/var/rmargin",
 	"./css/var/rnumnonpx",
 	"./css/var/cssExpand",
 	"./css/var/isHidden",
 	"./css/var/getStyles",
 	"./css/curCSS",
+	"./css/adjustCSS",
 	"./css/defaultDisplay",
 	"./css/addGetHookIf",
 	"./css/support",
@@ -17,16 +19,15 @@ define([
 	"./css/swap",
 	"./core/ready",
 	"./selector" // contains
-], function( jQuery, pnum, access, rmargin, rnumnonpx, cssExpand, isHidden,
-	getStyles, curCSS, defaultDisplay, addGetHookIf, support, dataPriv ) {
+], function( jQuery, pnum, rfxnum, access, rmargin, rnumnonpx, cssExpand, isHidden,
+	getStyles, curCSS, adjustCSS, defaultDisplay, addGetHookIf, support, dataPriv ) {
 
 var
 	// Swappable if display is none or starts with table
 	// except "table", "table-cell", or "table-caption"
 	// See here for display values: https://developer.mozilla.org/en-US/docs/CSS/display
 	rdisplayswap = /^(none|table(?!-c[ea]).+)/,
 	rnumsplit = new RegExp( "^(" + pnum + ")(.*)$", "i" ),
-	rrelNum = new RegExp( "^([+-])=(" + pnum + ")", "i" ),
 
 	cssShow = { position: "absolute", visibility: "hidden", display: "block" },
 	cssNormalTransform = {
@@ -272,8 +273,8 @@ jQuery.extend({
 			type = typeof value;
 
 			// Convert "+=" or "-=" to relative numbers (#7345)
-			if ( type === "string" && (ret = rrelNum.exec( value )) ) {
-				value = ( ret[1] + 1 ) * ret[2] + parseFloat( jQuery.css( elem, name ) );
+			if ( type === "string" && (ret = rfxnum.exec( value )) && ret[ 1 ] ) {
+				value = adjustCSS( elem, name, ret );
 				// Fixes bug #9237
 				type = "number";
 			}
@@ -283,9 +284,13 @@ jQuery.extend({
 				return;
 			}
 
-			// If a number was passed in, add 'px' (except for certain CSS properties)
-			if ( type === "number" && !jQuery.cssNumber[ origName ] ) {
-				value += "px";
+			// If a number was passed in, add the unit (except for certain CSS properties)
+			if ( type === "number" ) {
+				if ( ret && ret[ 3 ] ) {
+					value += ret[ 3 ];
+				} else if ( !jQuery.cssNumber[ origName ] ) {
+					value += "px";
+				}
 			}
 
 			// Support: IE9-11+

src/css/adjustCSS.js

@@ -0,0 +1,60 @@
+define([
+	"../core",
+	"../var/rfxnum"
+], function( jQuery, rfxnum ) {
+
+function adjustCSS( elem, prop, value, tween ) {
+	var adjusted,
+		scale = 1,
+		maxIterations = 20,
+		currentValue = tween ?
+			function() { return tween.cur(); } :
+			function() { return jQuery.css( elem, prop, "" ); },
+		initial = currentValue(),
+		unit = value && value[ 3 ] || ( jQuery.cssNumber[ prop ] ? "" : "px" ),
+		// Starting value computation is required for potential unit mismatches
+		recasted = ( jQuery.cssNumber[ prop ] || unit !== "px" && +initial ) &&
+			rfxnum.exec( jQuery.css( elem, prop ) );
+
+	if ( recasted && recasted[ 3 ] !== unit ) {
+		// Trust units reported by jQuery.css
+		unit = unit || recasted[ 3 ];
+
+		// Make sure we update the tween properties later on
+		value = value || [];
+
+		// Iteratively approximate from a nonzero starting point
+		recasted = +initial || 1;
+
+		do {
+			// If previous iteration zeroed out, double until we get *something*.
+			// Use string for doubling so we don't accidentally see scale as unchanged below
+			scale = scale || ".5";
+
+			// Adjust and apply
+			recasted = recasted / scale;
+			jQuery.style( elem, prop, recasted + unit );
+
+		// Update scale, tolerating zero or NaN from tween.cur()
+		// Break the loop if scale is unchanged or perfect, or if we've just had enough.
+		} while (
+			scale !== (scale = currentValue() / initial) && scale !== 1 && --maxIterations
+		);
+	}
+
+	if ( value ) {
+		recasted = +recasted || +initial || 0;
+		adjusted = value[ 1 ] ?
+			recasted + ( value[ 1 ] + 1 ) * value[ 2 ] :
+			+value[ 2 ];
+		if ( tween ) {
+			tween.unit = unit;
+			tween.start = recasted;
+			tween.end = adjusted;
+		}
+	}
+	return adjusted;
+}
+
+return adjustCSS;
+});

src/effects.js

@@ -1,9 +1,10 @@
 define([
 	"./core",
 	"./var/document",
-	"./var/pnum",
+	"./var/rfxnum",
 	"./css/var/cssExpand",
 	"./css/var/isHidden",
+	"./css/adjustCSS",
 	"./css/defaultDisplay",
 	"./data/var/dataPriv",
 
@@ -13,63 +14,18 @@ define([
 	"./css",
 	"./deferred",
 	"./traversing"
-], function( jQuery, document, pnum, cssExpand, isHidden, defaultDisplay, dataPriv ) {
+], function( jQuery, document, rfxnum, cssExpand,
+	isHidden, adjustCSS, defaultDisplay, dataPriv ) {
 
 var
 	fxNow, timerId,
 	rfxtypes = /^(?:toggle|show|hide)$/,
-	rfxnum = new RegExp( "^(?:([+-])=|)(" + pnum + ")([a-z%]*)$", "i" ),
 	rrun = /queueHooks$/,
 	animationPrefilters = [ defaultPrefilter ],
 	tweeners = {
 		"*": [ function( prop, value ) {
-			var tween = this.createTween( prop, value ),
-				target = tween.cur(),
-				parts = rfxnum.exec( value ),
-				unit = parts && parts[ 3 ] || ( jQuery.cssNumber[ prop ] ? "" : "px" ),
-
-				// Starting value computation is required for potential unit mismatches
-				start = ( jQuery.cssNumber[ prop ] || unit !== "px" && +target ) &&
-					rfxnum.exec( jQuery.css( tween.elem, prop ) ),
-				scale = 1,
-				maxIterations = 20;
-
-			if ( start && start[ 3 ] !== unit ) {
-				// Trust units reported by jQuery.css
-				unit = unit || start[ 3 ];
-
-				// Make sure we update the tween properties later on
-				parts = parts || [];
-
-				// Iteratively approximate from a nonzero starting point
-				start = +target || 1;
-
-				do {
-					// If previous iteration zeroed out, double until we get *something*.
-					// Use string for doubling so we don't accidentally see scale as unchanged below
-					scale = scale || ".5";
-
-					// Adjust and apply
-					start = start / scale;
-					jQuery.style( tween.elem, prop, start + unit );
-
-				// Update scale, tolerating zero or NaN from tween.cur(),
-				// break the loop if scale is unchanged or perfect, or if we've just had enough
-				} while (
-					scale !== (scale = tween.cur() / target) && scale !== 1 && --maxIterations
-				);
-			}
-
-			// Update tween properties
-			if ( parts ) {
-				start = tween.start = +start || +target || 0;
-				tween.unit = unit;
-				// If a +=/-= token was provided, we're doing a relative animation
-				tween.end = parts[ 1 ] ?
-					start + ( parts[ 1 ] + 1 ) * parts[ 2 ] :
-					+parts[ 2 ];
-			}
-
+			var tween = this.createTween( prop, value );
+			adjustCSS( tween.elem, prop, rfxnum.exec( value ), tween );
 			return tween;
 		} ]
 	};

src/var/rfxnum.js

@@ -0,0 +1,7 @@
+define([
+	"../var/pnum"
+], function( pnum ) {
+
+return new RegExp( "^(?:([+-])=|)(" + pnum + ")([a-z%]*)$", "i" );
+
+});

test/unit/css.js

@@ -203,6 +203,59 @@ test( "css() explicit and relative values", 29, function() {
 	equal( $elem.css("opacity"), "1", "'+=0.5' on opacity (params)" );
 });
 
+test( "css() non-px relative values (gh-1711)", 17, function() {
+	var cssCurrent,
+		units = {},
+		$parent = jQuery("#nothiddendiv"),
+		$child = jQuery("#nothiddendivchild", $parent),
+		add = function( prop, val, unit ) {
+			var str = ( val < 0 ? "-=" : "+=" ) + Math.abs(val) + unit;
+			$child.css( prop, str );
+			equal(
+				Math.round( parseFloat( $child.css( prop ) ) ),
+				Math.round( cssCurrent += val * units[ prop ][ unit ] ),
+				"'" + str + "' on " + prop
+			);
+		},
+		getUnits = function( prop ) {
+			units[ prop ] = {
+				"px": 1,
+				"em": parseFloat( $child.css( "fontSize", "16px" ).css( "fontSize" )),
+				"pt": parseFloat( $child.css( prop, "100pt" ).css( prop ) ) / 100,
+				"pc": parseFloat( $child.css( prop, "100pc" ).css( prop ) ) / 100,
+				"cm": parseFloat( $child.css( prop, "100cm" ).css( prop ) ) / 100,
+				"mm": parseFloat( $child.css( prop, "100mm" ).css( prop ) ) / 100,
+				"%" : parseFloat( $child.css( prop, "100%"  ).css( prop ) ) / 100
+			};
+		};
+
+	$parent.css({ height: 1, padding: 0, width: 400 });
+	$child.css({ height: 1, padding: 0 });
+
+	getUnits( "width" );
+	cssCurrent = $child.css( "width", "50%" ).width();
+	add( "width",  25,    "%" );
+	add( "width", -50,    "%" );
+	add( "width",  10,   "em" );
+	add( "width",  10,   "pt" );
+	add( "width",  -2.3, "pt" );
+	add( "width",   5,   "pc" );
+	add( "width",  -5,   "em" );
+	add( "width",  +2,   "cm" );
+	add( "width", -15,   "mm" );
+	add( "width",  21,   "px" );
+
+	getUnits( "lineHeight" );
+	cssCurrent = parseFloat( $child.css( "lineHeight", "1em" ).css( "lineHeight" ) );
+	add( "lineHeight",   2, "em" );
+	add( "lineHeight", -10, "px" );
+	add( "lineHeight",  20, "pt" );
+	add( "lineHeight",  30, "pc" );
+	add( "lineHeight",   1, "cm" );
+	add( "lineHeight", -20, "mm" );
+	add( "lineHeight",  50,  "%" );
+});
+
 test("css(String, Object)", function() {
 	expect( 19 );
 	var j, div, display, ret, success;