feat(is-visible): add support for clip-path techniques

lib/commons/dom/is-visible.js

@@ -1,21 +1,39 @@
 /* global dom */
+const clipRegex = /rect\s*\(([0-9]+)px,?\s*([0-9]+)px,?\s*([0-9]+)px,?\s*([0-9]+)px\s*\)/;
+const clipPathRegex = /(\w+)\((\d+)/;
 
 /**
- * Determines if an element is hidden with the clip rect technique
+ * Determines if an element is hidden with a clip or clip-path technique
  * @method isClipped
  * @memberof axe.commons.dom
  * @private
- * @param  {String}  clip Computed property value of clip
+ * @param  {CSSStyleDeclaration} style Computed style
  * @return {Boolean}
  */
-function isClipped(clip) {
+function isClipped(style) {
 	'use strict';
 
-	var matches = clip.match(
-		/rect\s*\(([0-9]+)px,?\s*([0-9]+)px,?\s*([0-9]+)px,?\s*([0-9]+)px\s*\)/
-	);
-	if (matches && matches.length === 5) {
-		return matches[3] - matches[1] <= 0 && matches[2] - matches[4] <= 0;
+	const matchesClip = style.getPropertyValue('clip').match(clipRegex);
+	const matchesClipPath = style
+		.getPropertyValue('clip-path')
+		.match(clipPathRegex);
+	if (matchesClip && matchesClip.length === 5) {
+		return (
+			matchesClip[3] - matchesClip[1] <= 0 &&
+			matchesClip[2] - matchesClip[4] <= 0
+		);
+	}
+	if (matchesClipPath) {
+		const type = matchesClipPath[1];
+		const value = parseInt(matchesClipPath[2], 10);
+
+		switch (type) {
+			case 'inset':
+				return value >= 50;
+			case 'circle':
+				return value === 0;
+			default:
+		}
 	}
 
 	return false;
@@ -60,7 +78,7 @@ dom.isVisible = function(el, screenReader, recursed) {
 	if (
 		style.getPropertyValue('display') === 'none' ||
 		['STYLE', 'SCRIPT', 'NOSCRIPT', 'TEMPLATE'].includes(nodeName) ||
-		(!screenReader && isClipped(style.getPropertyValue('clip'))) ||
+		(!screenReader && isClipped(style)) ||
 		(!recursed &&
 			// visibility is only accurate on the first element
 			(style.getPropertyValue('visibility') === 'hidden' ||

test/commons/dom/is-visible.js

@@ -3,6 +3,7 @@ describe('dom.isVisible', function() {
 
 	var fixture = document.getElementById('fixture');
 	var fixtureSetup = axe.testUtils.fixtureSetup;
+	var isIE11 = axe.testUtils.isIE11;
 	var shadowSupported = axe.testUtils.shadowSupport.v1;
 	var fakeNode = {
 		nodeType: Node.ELEMENT_NODE,
@@ -188,6 +189,33 @@ describe('dom.isVisible', function() {
 			el = document.getElementById('target');
 			assert.isFalse(axe.commons.dom.isVisible(el));
 		});
+
+		// IE11 either only supports clip paths defined by url() or not at all,
+		// MDN and caniuse.com give different results...
+		(isIE11 || window.PHANTOMJS ? it.skip : it)(
+			'should detect clip-path hidden text technique',
+			function() {
+				fixture.innerHTML =
+					'<div id="target" style="clip-path: inset(50%);">Hi</div>';
+
+				var el = document.getElementById('target');
+				assert.isFalse(axe.commons.dom.isVisible(el));
+			}
+		);
+
+		(isIE11 || window.PHANTOMJS ? it.skip : it)(
+			'should detect clip-path hidden text technique on parent',
+			function() {
+				fixture.innerHTML =
+					'<div style="clip-path: circle(0%);">' +
+					'<div id="target">Hi</div>' +
+					'</div>';
+
+				var el = document.getElementById('target');
+				assert.isFalse(axe.commons.dom.isVisible(el));
+			}
+		);
+
 		(shadowSupported ? it : xit)(
 			'should correctly handle visible slotted elements',
 			function() {
@@ -411,5 +439,23 @@ describe('dom.isVisible', function() {
 			el = document.getElementById('target');
 			assert.isTrue(axe.commons.dom.isVisible(el, true));
 		});
+
+		it('should detect clip-path hidden text technique', function() {
+			fixture.innerHTML =
+				'<div id="target" style="clip-path: inset(50%);">Hi</div>';
+
+			var el = document.getElementById('target');
+			assert.isTrue(axe.commons.dom.isVisible(el, true));
+		});
+
+		it('should detect clip-path hidden text technique on parent', function() {
+			fixture.innerHTML =
+				'<div style="clip-path: circle(0%);">' +
+				'<div id="target">Hi</div>' +
+				'</div>';
+
+			var el = document.getElementById('target');
+			assert.isTrue(axe.commons.dom.isVisible(el, true));
+		});
 	});
 });