Added Source code to javascript intro video

content/batch/learn/js/dom.mdx

@@ -61,4 +61,90 @@ Want to improve this page?. Raise a issue on [@github](https://github.com/Manish
 
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-</Tabs>
+</Tabs>
+
+## Notes
+
+# JavaScript DOM Cheatsheet
+
+### What is DOM?
+
+The Document Object Model (DOM) is a programming interface for HTML documents. It represents the page so that programs can change the document structure, style, and content.
+
+## DOM Methods to find HTML elements:
+
+### Get Element by Id
+
+Returns the element that has the ID attribute with the specified value.
+
+```jsx
+let element = document.getElementById("myElement");
+```
+
+### Get Elements By Class Name
+
+Returns a collection of all elements in the document with the specified class name.
+
+```jsx
+let elements = document.getElementsByClassName("myClass");
+```
+
+### Get Elements By Tag Name
+
+Returns a collection of all elements in the document with the specified tag name.
+
+```jsx
+let elements = document.getElementsByTagName("p");
+```
+
+### Query Selector All
+
+Returns all elements that matches a specified CSS selector(s) in the document
+
+```jsx
+let elements = document.querySelectorAll(".myClass");
+```
+
+### InnerHTML
+
+Gets or sets the HTML content within an element.
+
+```jsx
+element.innerHTML = "<p>New HTML content</p>";
+```
+
+### InnerText
+
+Gets or sets the text content within an element.
+
+```jsx
+element.innerText = "New text content";
+```
+
+### Add Class
+
+Adds one or more class names to an element.
+
+```jsx
+element.classList.add("newClass");
+```
+
+### Remove Class
+
+Removes one or more class names from an element.
+
+```jsx
+element.classList.remove("oldClass");
+```
+
+### Add Event Listener
+
+Attaches an event handler to the specified element.
+
+```jsx
+const myButton = document.getElementById("myButton");
+
+myButton.addEventListener("click", function() {
+  console.log("Button clicked!");
+});
+```