Implement NodeStore

Author: ayush013

challenges/DOM.md

@@ -6,6 +6,7 @@
 
 1. [Show the different ways of selecting an element from DOM](#Q1)
 1. [Show the ways to loop over the Nodelist obtained after querying for the elements](#Q2)
+3. [Design and Implement a Node Store, which supports DOM element as key](#Q3)
 
 ---
 
@@ -43,4 +44,50 @@ Note goes here
 
 <br />
 
+
+#### Q3
+### Design and Implement a Node Store, which supports DOM element as key
+
+- Implement it without using inbuilt Map
+- Can you do it in O(1) Time complexity?
+
+```js
+class NodeStore {
+
+  constructor() {
+    this.store = {};
+  }
+   /**
+   * @param {Node} node
+   * @param {any} value
+   */
+  set(node, value) {
+   node.__nodeIdentifier__ = Symbol();
+   this.store[node.__nodeIdentifier__] = value
+  }
+  /**
+   * @param {Node} node
+   * @return {any}
+   */
+  get(node) {
+    return this.store[node.__nodeIdentifier__];
+  }
+  
+  /**
+   * @param {Node} node
+   * @return {Boolean}
+   */
+  has(node) {
+    return !!this.store[node.__nodeIdentifier__];
+  }
+}
+```
+
+###### References
+- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
+
+<br />
+
+
+
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