feat: add AbstractVirtualNode for linting (#1627)

* feat: add AbstractVirtualNode for linting

* create typescript interface and test

* remove typescript for now

* forgot one

Author: straker

lib/core/base/virtual-node.js

@@ -1,15 +1,42 @@
 const whitespaceRegex = /[\t\r\n\f]/g;
 
+class AbstractVirtualNode {
+	constructor() {
+		this.children = [];
+		this.parent = null;
+	}
+
+	get props() {
+		throw new Error(
+			'VirtualNode class must have a "props" object consisting ' +
+				'of "nodeType" and "nodeName" properties'
+		);
+	}
+
+	hasClass() {
+		throw new Error('VirtualNode class must have a "hasClass" function');
+	}
+
+	attr() {
+		throw new Error('VirtualNode class must have a "attr" function');
+	}
+
+	hasAttr() {
+		throw new Error('VirtualNode class must have a "hasAttr" function');
+	}
+}
+
 // class is unused in the file...
 // eslint-disable-next-line no-unused-vars
-class VirtualNode {
+class VirtualNode extends AbstractVirtualNode {
 	/**
 	 * Wrap the real node and provide list of the flattened children
 	 * @param {Node} node the node in question
 	 * @param {VirtualNode} parent The parent VirtualNode
 	 * @param {String} shadowId the ID of the shadow DOM to which this node belongs
 	 */
 	constructor(node, parent, shadowId) {
+		super();
 		this.shadowId = shadowId;
 		this.children = [];
 		this.actualNode = node;
@@ -105,3 +132,5 @@ class VirtualNode {
 		return this._cache.tabbableElements;
 	}
 }
+
+axe.AbstractVirtualNode = AbstractVirtualNode;

test/core/base/virtual-node.js

@@ -7,6 +7,56 @@ describe('VirtualNode', function() {
 		node = document.createElement('div');
 	});
 
+	describe('AbstractVirtualNode', function() {
+		it('should be a function', function() {
+			assert.isFunction(axe.AbstractVirtualNode);
+		});
+
+		it('should throw an error when accessing props', function() {
+			function fn() {
+				var abstractNode = new axe.AbstractVirtualNode();
+				if (abstractNode.props.nodeType === 1) {
+					return;
+				}
+			}
+
+			assert.throws(fn);
+		});
+
+		it('should throw an error when accessing hasClass', function() {
+			function fn() {
+				var abstractNode = new axe.AbstractVirtualNode();
+				if (abstractNode.hasClass('foo')) {
+					return;
+				}
+			}
+
+			assert.throws(fn);
+		});
+
+		it('should throw an error when accessing attr', function() {
+			function fn() {
+				var abstractNode = new axe.AbstractVirtualNode();
+				if (abstractNode.attr('foo') === 'bar') {
+					return;
+				}
+			}
+
+			assert.throws(fn);
+		});
+
+		it('should throw an error when accessing hasAttr', function() {
+			function fn() {
+				var abstractNode = new axe.AbstractVirtualNode();
+				if (abstractNode.hasAttr('foo')) {
+					return;
+				}
+			}
+
+			assert.throws(fn);
+		});
+	});
+
 	it('should be a function', function() {
 		assert.isFunction(VirtualNode);
 	});