Add Element#replaceChild(), tests and a fix for insertBefore()

src/undom.js

@@ -39,11 +39,18 @@ export default function undom() {
 		insertBefore(child, ref) {
 			child.remove();
 			let i = splice(this.childNodes, ref, child);
-			if (child.nodeType===1) {
-				while (i<this.childNodes.length && (ref = this.childNodes[i]).nodeType!==1) i++;
+			if (!ref) this.appendChild(child);
+			else if (~i && child.nodeType===1) {
+				while (i<this.childNodes.length && (ref = this.childNodes[i]).nodeType!==1 || ref===child) i++;
 				if (ref) splice(this.children, ref, child);
 			}
 		}
+		replaceChild(child, ref) {
+			if (ref.parentNode===this) {
+				this.insertBefore(child, ref);
+				ref.remove();
+			}
+		}
 		removeChild(child) {
 			splice(this.childNodes, child);
 			if (child.nodeType===1) splice(this.children, child);

test/undom.js

@@ -74,6 +74,27 @@ describe('undom', () => {
 			});
 		});
 
+		describe('#replaceChild()', () => {
+			it('should replace a child', () => {
+				let parent = document.createElement('div');
+				let child1 = document.createElement('child1');
+				let child2 = document.createElement('child2');
+				let child3 = document.createElement('child3');
+				let child4 = document.createElement('child4');
+				parent.appendChild(child1);
+				parent.appendChild(child2);
+				parent.appendChild(child3);
+
+				expect(parent).to.have.property('childNodes').eql([child1, child2, child3]);
+				expect(parent).to.have.property('children').eql([child1, child2, child3]);
+
+				parent.replaceChild(child4, child2);
+
+				expect(parent).to.have.property('childNodes').eql([child1, child4, child3]);
+				expect(parent).to.have.property('children').eql([child1, child4, child3]);
+			});
+		});
+
 		describe('#setAttribute()', () => {
 			it('should set a given named attribute', () => {
 				let el = document.createElement('div');