The term **Virtual DOM** is commonly used to describe [React](/courses/reactjs)'s in-memory representation of what the UI should look like before changes are committed to the browser DOM. It is best treated as a conceptual model rather than a separate browser feature or API that developers directly manipulate. ### Why Does React Need an In-Memory UI Description? Consider this component: ```jsx function Profile({ user }) { return (

{user.name}

{user.role}

); } ``` [React](/courses/reactjs) evaluates the component and creates an internal representation describing the UI structure. Conceptually: ```text section ├── h2 │ └── user.name └── p └── user.role ``` When data changes, React calculates a new UI description. ### Example Update Previous data: ```javascript { name: "Asif", role: "Developer" } ``` New data: ```javascript { name: "Asif", role: "Admin" } ``` Conceptually React sees: ```text Previous UI section ├── h2 → Asif └── p → Developer Next UI section ├── h2 → Asif └── p → Admin ``` The structure is mostly unchanged. Only the role text needs a DOM update. ### Virtual DOM Does Not Mean React Copies the Entire Browser DOM A common misconception is: ```text React clones the full browser DOM after every update ``` That is not a useful way to understand React. React maintains its own internal component and element representation, calculates what the UI should become, and then updates the host environment such as the browser DOM where necessary. ### Why Not Directly Change the DOM Everywhere? Without React, application code might manually perform operations such as: ```javascript document.querySelector("#username").textContent = user.name; document.querySelector("#role").textContent = user.role; ``` As interfaces become complex, developers would need to manually track which DOM elements correspond to which state changes. React instead lets you describe the desired UI: ```jsx

{user.name}

{user.role}

``` React handles how that description becomes DOM updates. ### Declarative Mental Model ```text Application state ↓ React components ↓ UI description ↓ Reconciliation ↓ Required DOM changes ``` ### Is the Virtual DOM Automatically Faster Than Every Direct DOM Approach? No. A carefully written direct DOM operation can be extremely fast. React's major benefit is that developers can describe UI declaratively while React coordinates updates efficiently and consistently across complex component trees. Performance depends on the application and the work being performed. ### Interview-Ready Answer The Virtual DOM is a common term for React's in-memory representation of the desired UI. When state or props change, React creates the next UI representation, reconciles it with the previous one, and commits only the necessary changes to the real DOM. Its main value is enabling React's declarative programming model and efficient update coordination rather than guaranteeing that every React update is faster than direct DOM manipulation.