React vs traditional JavaScript - Quick Revision & Key Differences

Recall & Review

beginner

What is the main difference between React and traditional JavaScript when building user interfaces?

React uses components to build UI in a structured and reusable way, while traditional JavaScript manipulates the DOM directly and often mixes HTML, CSS, and JS in less organized ways.

intermediate

How does React improve updating the user interface compared to traditional JavaScript?

React uses a virtual DOM to efficiently update only the parts of the UI that change, avoiding slow full page or large DOM updates common in traditional JavaScript.

beginner

What role do components play in React compared to functions in traditional JavaScript?

Components in React are like building blocks that manage their own content and state, making UI easier to build and maintain, unlike traditional JS functions which often just run code without UI structure.

beginner

Why is JSX important in React compared to traditional JavaScript?

JSX lets you write HTML-like code inside JavaScript, making UI code clearer and easier to understand, while traditional JavaScript requires manual DOM creation and manipulation.

intermediate

How does React handle state differently than traditional JavaScript?

React uses hooks like useState to keep track of data that changes over time and automatically updates the UI, whereas traditional JavaScript requires manual DOM updates when data changes.

What does React use to efficiently update the UI?

A CSS animations

B Direct DOM manipulation

C jQuery selectors

D Virtual DOM

React uses a virtual DOM to update only the parts of the UI that change, improving performance.

In React, what is JSX used for?

A Writing HTML-like code inside JavaScript

B Styling components

C Fetching data from APIs

D Managing browser cookies

JSX allows writing HTML-like syntax directly in JavaScript, making UI code easier to read and write.

Which of these is a key feature of React components?

A They run server-side only

B They manage their own state and UI

C They replace HTML tags in the browser

D They only handle CSS styling

React components manage their own state and UI, making them reusable and organized.

How does traditional JavaScript usually update the UI?

A By directly changing the DOM elements

B Using virtual DOM

C With React hooks

D Through JSX syntax

Traditional JavaScript updates the UI by directly manipulating DOM elements.

What React hook is commonly used to handle changing data in components?

A useEffect

B useContext

C useState

D useRef

useState is the React hook used to manage state and update the UI when data changes.

Explain how React's approach to building user interfaces differs from traditional JavaScript.

Think about how React organizes UI and updates it compared to manual DOM changes.

Describe the benefits of using React components over traditional JavaScript functions for UI development.

Consider how components help keep UI code organized and manageable.

Practice

1. What is a key difference between React and traditional JavaScript when building web pages?

easy

A. React requires writing HTML only, traditional JavaScript uses CSS only.

B. React uses components and JSX, while traditional JavaScript manipulates the DOM directly.

C. React cannot update the page dynamically, traditional JavaScript can.

D. React uses server-side rendering only, traditional JavaScript is client-side only.

Solution

1. Step 1: Understand React's approach

   React builds UI using components and JSX, which is a syntax that looks like HTML inside JavaScript.

2. Step 2: Understand traditional JavaScript approach

   Traditional JavaScript changes the page by directly manipulating the DOM elements, which can be more complex and error-prone.

3. Final Answer:

   React uses components and JSX, while traditional JavaScript manipulates the DOM directly. -> Option B

4. Quick Check:

   React uses components and JSX = A [OK]

Hint: React uses components; traditional JS changes DOM directly [OK]

Common Mistakes:

• Thinking React only uses HTML or CSS
• Believing React cannot update pages dynamically
• Confusing server-side and client-side rendering

2. Which of the following is the correct way to create a React functional component?

easy

A. class MyComponent extends React.Component { render() { return 'Hello'; } }

B. var MyComponent = Hello;

C. function MyComponent() { return Hello; }

D. function MyComponent() { document.write('Hello'); }

Solution

1. Step 1: Identify React functional component syntax

   A React functional component is a function returning JSX, like function MyComponent() { return <div>Hello</div>; }.

2. Step 2: Check other options for correctness

   var MyComponent =
   Hello; assigns JSX directly to a variable, not a function. class MyComponent extends React.Component { render() { return 'Hello'; } } is a class component, not functional. function MyComponent() { document.write('Hello'); } uses document.write, which is not React.

3. Final Answer:

   function MyComponent() { return <div>Hello</div>; } -> Option C

4. Quick Check:

   Functional component returns JSX function = A [OK]

Hint: Functional components are functions returning JSX [OK]

Common Mistakes:

• Confusing class components with functional components
• Using document.write inside React components
• Assigning JSX to variables without functions

3. What will be the output on the page when this React component is rendered?

function Greeting() {
  const name = 'Alice';
  return <h1>Hello, {name}!</h1>;
}

medium

A. Hello, Alice!

B. Hello, name!

C. <h1>Hello, {name}!</h1>

D. Error: name is not defined

Solution

1. Step 1: Understand JSX expression evaluation

   Inside JSX, curly braces {name} insert the value of the variable name, which is 'Alice'.

2. Step 2: Determine rendered output

   The component returns <h1>Hello, Alice!</h1>, so the page shows the text 'Hello, Alice!'.

3. Final Answer:

   Hello, Alice! -> Option A

4. Quick Check:

   JSX inserts variable value = C [OK]

Hint: JSX {variable} shows variable value, not text {variable} [OK]

Common Mistakes:

• Thinking JSX shows {name} literally
• Confusing variable name with string output
• Expecting an error due to variable usage

4. Identify the error in this React component code:

function Counter() {
  let count = 0;
  function increment() {
    count++;
  }
  return <button onClick={increment}>Count: {count}</button>;
}

medium

A. Using let instead of const for count

B. onClick should be written as onclick

C. Missing semicolon after count++

D. The increment function does not update the displayed count

Solution

1. Step 1: Understand React state behavior

   React components must use state (like useState) to update UI dynamically. Here, count is a normal variable and changes won't re-render the component.

2. Step 2: Identify why increment doesn't update UI

   Increment changes count variable but React does not know to re-render, so displayed count stays 0.

3. Final Answer:

   The increment function does not update the displayed count -> Option D

4. Quick Check:

   State needed to update UI = D [OK]

Hint: Use React state (useState) to update UI, not plain variables [OK]

Common Mistakes:

• Thinking let vs const affects UI update
• Ignoring React's re-render on state change
• Using wrong event attribute case

5. You want to build a dynamic list of items that updates when a user adds a new item. Which approach best uses React instead of traditional JavaScript?

hard

A. Use React's useState hook to store the list and update it, then render the list in JSX.

B. Use document.getElementById to find the list element and append new items manually.

C. Write a for loop to create HTML strings and set innerHTML of the list container.

D. Use React class components with componentDidMount to update the list directly.

Solution

1. Step 1: Understand React's dynamic UI approach

   React uses state (like useState) to hold data and re-renders UI automatically when state changes.

2. Step 2: Compare with traditional DOM manipulation

   Traditional JavaScript manipulates DOM directly (options A and C), which is harder to manage and less efficient.

3. Step 3: Consider React class components

   Use React class components with componentDidMount to update the list directly. uses class components and lifecycle methods, but modern React prefers functional components with hooks.

4. Final Answer:

   Use React's useState hook to store the list and update it, then render the list in JSX. -> Option A

5. Quick Check:

   React state and JSX rendering = B [OK]

Hint: Use useState hook for dynamic lists in React [OK]

Common Mistakes:

• Using direct DOM methods inside React components
• Relying on innerHTML string building
• Using outdated class components instead of hooks