Implementing a Custom Virtual DOM - Part II Deserialize

In the previous blog, we explored how to serialize the real DOM into a Virtual DOM (VDOM). Now, in the second part of our series, we'll take the next step: deserializing the Virtual DOM back into actual DOM elements. This process is essential for rendering the Virtual DOM into the real DOM or updating the DOM based on changes in the Virtual DOM.

Recap: What is a Virtual DOM?

The Virtual DOM is an in-memory representation of the actual DOM. It enables efficient updates by comparing the current Virtual DOM with a previous version and applying only the necessary changes to the real DOM. In this episode, we will focus on converting a Virtual DOM object back into real DOM elements.

Real Interview Insights

Interviewers might ask you to:

• Implement a function that can deserialize or convert a Virtual DOM object back into actual DOM nodes.
• Understand how to handle different node types, including elements and text nodes.
• Ensure that the attributes and properties of the Virtual DOM nodes are correctly applied to the real DOM nodes.

Implementing the Virtual DOM Deserializer

We’ll create a function that takes a Virtual DOM object and converts it into a real DOM element that can be inserted into the document.

Step 1: Define the deserialize Function

The deserialize function will traverse the Virtual DOM object, create corresponding real DOM nodes, and set their attributes and properties.

function deserialize(vNode) {
  if (vNode.type === 'text') {
    return document.createTextNode(vNode.props.nodeValue);
  }
 
  const element = document.createElement(vNode.type);
 
  // Set attributes/properties
  for (const prop in vNode.props) {
    element.setAttribute(prop, vNode.props[prop]);
  }
 
  // Recursively create and append child nodes
  vNode.children.forEach(childVNode => {
    element.appendChild(deserialize(childVNode));
  });
 
  return element;
}

Explanation:

• Handling Text Nodes: If the vNode is of type 'text', the function creates a text node using document.createTextNode with the value from vNode.props.nodeValue.
• Creating Element Nodes: For element nodes, the function uses document.createElement to create the DOM element and then applies attributes from vNode.props using setAttribute.
• Handling Children: The function recursively deserializes and appends child nodes to the created element.

Step 2: Example Usage

Let’s see how the deserialize function works with a previously serialized Virtual DOM object.

// Example Virtual DOM structure
const vDOM = {
  type: 'div',
  props: { id: 'app' },
  children: [
    {
      type: 'h1',
      props: { class: 'title' },
      children: [
        {
          type: 'text',
          props: { nodeValue: 'Hello, Virtual DOM!' },
          children: []
        }
      ]
    },
    {
      type: 'p',
      props: {},
      children: [
        {
          type: 'text',
          props: { nodeValue: 'Welcome to the world of Virtual DOM.' },
          children: []
        }
      ]
    }
  ]
};
 
// Deserialize the Virtual DOM to actual DOM elements
const realDOM = deserialize(vDOM);
 
// Append the resulting DOM to the document body
document.body.appendChild(realDOM);

Explanation:

• Virtual DOM Structure: The example vDOM object represents a simple structure with a div element containing an h1 and a p element.
• Deserialization: The deserialize function converts the vDOM object into real DOM elements.
• Appending to the Document: Finally, the resulting DOM elements are appended to the document body, rendering them on the page.

Handling Edge Cases

1. Attributes with Special Values: Attributes such as class, id, and data-* should be handled correctly. Ensure the attributes are set appropriately on the DOM elements.
2. Empty Elements: Handle elements that do not have children or attributes, ensuring they are still correctly created and inserted into the DOM.
3. Nested Structures: The recursive nature of the deserialize function ensures that deeply nested structures are properly handled and rendered.

Use Cases for Virtual DOM Deserialization

1. Initial Rendering: Deserialization is key to the initial rendering of a Virtual DOM structure into the real DOM.
2. Server-Side Rendering: When sending a Virtual DOM from the server, deserialization allows the client to convert it into the real DOM.
3. UI Libraries: Virtual DOM deserialization is fundamental in libraries like React, where it’s used to render UI components efficiently.