Create HTML to DOM helper for the client/browser

The original HTML to DOM helper works in the node environment
and it depends on both `htmlparser2` and `domhandler`, which is
unnecessary in the browser environment because there is already
a DOM provided.

As a result, the motivation is to create a helper that if on the
client-side, uses the DOM API to prevent bundling the extra node
modules in the build. This is to keep the library isomorphic.

`formatDOM` ensures that the NodeLists are formatted like the
output from `htmlparser2.parseDOM`.

The contract is as specified:
```js
{
  type: "tag" || "script" || "style" || "text" || "comment",
  [ name: [String], ]
  [ data: [String], ]
  [ attribs: [Object], ]
  [ children: [Array], ]
  next: [Object] || null,
  prev: [Object] || null,
  parent: [Circular] || null
}
```

Author: remarkablemark

lib/html-to-dom-client.js

@@ -0,0 +1,99 @@
+'use strict';
+
+/**
+ * Format the browser DOM attributes.
+ *
+ * @param  {NamedNodeMap} - The attributes.
+ * @return {Object}
+ */
+function formatAttributes(attributes) {
+    var result = {};
+    var attribute;
+
+    // NamedNodeMap is array-like
+    for (var i = 0, len = attributes.length; i < len; i++) {
+        attribute = attributes[i];
+        result[attribute.name] = attribute.value;
+    }
+
+    return result;
+}
+
+/**
+ * Format the browser DOM nodes to match that of `htmlparser2.parseDOM`.
+ *
+ * @param  {NodeList} nodes        - The DOM nodes.
+ * @param  {Object}   [parentNode] - The parent node that's already formatted.
+ * @return {Object}
+ */
+function formatDOM(nodes, parentNode) {
+    var result = [];
+    var node;
+    var prevNode;
+    var nodeObj;
+
+    // NodeList is array-like
+    for (var i = 0, len = nodes.length; i < len; i++) {
+        node = nodes[i];
+        // reset
+        nodeObj = {
+            next: null,
+            prev: result[i - 1] || null,
+            parent: parentNode || null
+        };
+
+        // set the next node for the previous node (if applicable)
+        if (prevNode = result[i - 1]) {
+            prevNode.next = nodeObj;
+        }
+
+        // set the node name if it's not "#text" or "#comment"
+        // e.g., "div"
+        if (node.nodeName.indexOf('#') !== 0) {
+            nodeObj.name = node.nodeName.toLowerCase();
+
+            // also, type "tag" nodes have"attribs"
+            nodeObj.attribs = {}; // default
+            if (node.attributes && node.attributes.length) {
+                nodeObj.attribs = formatAttributes(node.attributes);
+            }
+        }
+
+        // set the node type
+        // e.g., "tag"
+        switch (node.nodeType) {
+            // 1 = element
+            case 1:
+                if (nodeObj.name === 'script' || nodeObj.name === 'style') {
+                    nodeObj.type = nodeObj.name;
+                } else {
+                    nodeObj.type = 'tag';
+                }
+                // recursively format the children
+                nodeObj.children = formatDOM(node.childNodes, nodeObj);
+                break;
+                // 2 = attribute
+                // 3 = text
+            case 3:
+                nodeObj.type = 'text';
+                nodeObj.data = node.nodeValue;
+                break;
+                // 8 = comment
+            case 8:
+                nodeObj.type = 'comment';
+                nodeObj.data = node.nodeValue;
+                break;
+            default:
+                break;
+        }
+
+        result.push(nodeObj);
+    }
+
+    return result;
+}
+
+/**
+ * Export HTML to DOM client helper.
+ */
+module.exports = formatDOM;