feat: implement Element.querySelector/querySelectorAll

src/dom/document.ts

@@ -114,6 +114,12 @@ export class Document extends Node {
     setLock(true);
   }
 
+  // Expose the document's NWAPI for Element's access to
+  // querySelector/querySelectorAll
+  get _nwapi() {
+    return this.#nwapi;
+  }
+
   get documentURI() {
     return this.#documentURI;
   }

src/dom/element.ts

@@ -1,6 +1,7 @@
 import { getLock } from "../constructor-lock.ts";
 import { fragmentNodesFromString } from "../deserialize.ts";
 import { Node, NodeType, Text } from "./node.ts";
+import { NodeList, nodeListMutatorSym } from "./node-list.ts";
 
 export class DOMTokenList extends Set<string> {
   contains(token: string): boolean {
@@ -261,6 +262,26 @@ export class Element extends Node {
     return prev;
   }
 
+  querySelector(selectors: string): Element | null {
+    if (!this.ownerDocument) {
+      throw new Error("Element must have an owner document");
+    }
+
+    return this.ownerDocument!._nwapi.first(selectors, this);
+  }
+
+  querySelectorAll(selectors: string): NodeList {
+    if (!this.ownerDocument) {
+      throw new Error("Element must have an owner document");
+    }
+
+    const nodeList = new NodeList();
+    const mutator = nodeList[nodeListMutatorSym]();
+    mutator.push(...this.ownerDocument!._nwapi.select(selectors, this))
+
+    return nodeList;
+  }
+
   // TODO: DRY!!!
   getElementById(id: string): Element | null {
     for (const child of this.childNodes) {