Adding prepend function on metal-dom

packages/metal-dom/src/domNamed.js

@@ -521,6 +521,34 @@ export function parent(element, selector) {
 	return closest(element.parentNode, selector);
 }
 
+/**
+ * Inserts a node before first child of the parent. If child is a HTML string
+ * it will be converted to document fragment before prepending it to the parent.
+ * @param {!Element} parent The node to prepend to.
+ * @param {!(Element|NodeList|string)} child The thing who must be prepended
+ * @return {!Element} The prepended child
+ */
+export function prepend(parent, child) {
+	if (isString(child)) {
+		child = buildFragment(child);
+	}
+
+	if (!isNodeListLike(child) && !isDefAndNotNull(parent.firstChild)) {
+		parent.appendChild(child);
+	}
+
+	if (isNodeListLike(child)) {
+		const childArr = Array.prototype.slice.call(child);
+		for (let i = 0; i < childArr.length; i++) {
+			parent.appendChild(childArr[i]);
+		}
+	} else {
+		parent.insertBefore(child, parent.firstChild);
+	}
+
+	return child;
+}
+
 /**
  * Registers a custom event.
  * @param {string} eventName The name of the custom event.

packages/metal-dom/test/dom.js

@@ -215,6 +215,66 @@ describe('dom', function() {
 			assert.strictEqual('myChild2', parent.childNodes[1].className);
 		});
 
+		it('should prepend an element into a div without first child', function() {
+			let parent = document.createElement('div');
+			let elem = dom.buildFragment('<p>Hello World</p>');
+
+			dom.prepend(parent, elem);
+
+			assert.strictEqual('<p>Hello World</p>', parent.innerHTML);
+		});
+
+		it('should prepend an element into a div', function() {
+			let parent = document.createElement('div');
+			let p = document.createElement('p');
+			let span = document.createElement('span');
+
+			dom.append(parent, p);
+			dom.prepend(parent, span);
+
+			assert.strictEqual(parent.innerHTML, '<span></span><p></p>');
+		});
+
+		it('should prepend a text into a div', function() {
+			let parent = document.createElement('div');
+
+			dom.append(parent, 'Some text');
+			dom.prepend(parent, 'Headline: ');
+
+			assert.strictEqual(parent.innerHTML, 'Headline: Some text');
+		});
+
+		it('should prepend a node list to parent element', function() {
+			let parent = document.createElement('div');
+
+			let childFrag = dom.buildFragment(
+				'<div class="myChild">el1</div><div class="myChild2">el2</div><div class="myChild3">el3</div>'
+			);
+
+			dom.prepend(parent, childFrag.childNodes);
+
+			assert.strictEqual(3, parent.childNodes.length);
+			assert.strictEqual('myChild', parent.childNodes[0].className);
+			assert.strictEqual('myChild2', parent.childNodes[1].className);
+			assert.strictEqual('myChild3', parent.childNodes[2].className);
+
+			let parent2 = document.createElement('div');
+
+			dom.prepend(
+				parent2,
+				dom.buildFragment(
+					'<div class="myChild"></div><div class="myChild2"></div><div class="myChild3"></div>'
+				).childNodes
+			);
+			dom.prepend(parent2, dom.buildFragment('<div class="container"></div>'));
+
+			assert.strictEqual(4, parent2.childNodes.length);
+			assert.strictEqual('container', parent2.childNodes[0].className);
+			assert.strictEqual('myChild', parent2.childNodes[1].className);
+			assert.strictEqual('myChild2', parent2.childNodes[2].className);
+			assert.strictEqual('myChild3', parent2.childNodes[3].className);
+		});
+
 		it('should replace an element with a requested element', function() {
 			let element1 = document.createElement('div');
 			let element2 = document.createElement('div');