Fix #12243, $("col").width() should return the column's width. Close gh-916.

src/css.js

@@ -2,6 +2,9 @@ var curCSS, iframe, iframeDoc,
 	ralpha = /alpha\([^)]*\)/i,
 	ropacity = /opacity=([^)]*)/,
 	rposition = /^(top|right|bottom|left)$/,
+	// swappable if display is none or starts with table except "table", "table-cell", or "table-caption"
+	// see here for display values: https://developer.mozilla.org/en-US/docs/CSS/display
+	rdisplayswap = /^(none|table(?!-c[ea]).+)/,
 	rmargin = /^margin/,
 	rnumsplit = new RegExp( "^(" + core_pnum + ")(.*)$", "i" ),
 	rnumnonpx = new RegExp( "^(" + core_pnum + ")(?!px)[a-z%]+$", "i" ),
@@ -493,12 +496,14 @@ jQuery.each([ "height", "width" ], function( i, name ) {
 	jQuery.cssHooks[ name ] = {
 		get: function( elem, computed, extra ) {
 			if ( computed ) {
-				if ( elem.offsetWidth !== 0 || curCSS( elem, "display" ) !== "none" ) {
-					return getWidthOrHeight( elem, name, extra );
-				} else {
+				// certain elements can have dimension info if we invisibly show them
+				// however, it must have a current display style that would benefit from this
+				if ( elem.offsetWidth === 0 && rdisplayswap.test( curCSS( elem, "display" ) ) ) {
 					return jQuery.swap( elem, cssShow, function() {
 						return getWidthOrHeight( elem, name, extra );
 					});
+				} else {
+					return getWidthOrHeight( elem, name, extra );
 				}
 			}
 		},

test/unit/dimensions.js

@@ -292,14 +292,15 @@ test("getting dimensions shouldnt modify runtimeStyle see #9233", function() {
 	$div.remove();
 });
 
-test( "getting dimensions of zero width/height table elements shouldn't alter dimensions", function() {
-	expect( 1 );
-
-	var table = jQuery("<table><tbody><tr><td></td><td>a</td></tr><tr><td></td><td>a</td></tr></tbody></table>").appendTo("#qunit-fixture"),
-		elem = table.find("tr:eq(0) td:eq(0)");
+test( "table dimensions", 2, function() {
+	var table = jQuery("<table><colgroup><col/><col/></colgroup><tbody><tr><td></td><td>a</td></tr><tr><td></td><td>a</td></tr></tbody></table>").appendTo("#qunit-fixture"),
+		tdElem = table.find("tr:eq(0) td:eq(0)"),
+		colElem = table.find("col:eq(1)").width( 300 );
 
 	table.find("td").css({ "margin": 0, "padding": 0 });
-	equal( elem.width(), elem.width(), "width() doesn't alter dimension values" );
+
+	equal( tdElem.width(), tdElem.width(), "width() doesn't alter dimension values of empty cells, see #11293" );
+	equal( colElem.width(), 300, "col elements have width(), see #12243" );
 });
 
 test("box-sizing:border-box child of a hidden elem (or unconnected node) has accurate inner/outer/Width()/Height()  see #10413", function() {