When to use SASS vs CSS-in-JS - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

When is SASS more suitable than CSS-in-JS?

Which scenario best fits using SASS instead of CSS-in-JS?

A A React app where styles depend on component state and props.

B A large static website with minimal JavaScript and many global styles.

C A project requiring dynamic theming based on user interaction.

D A single-page app with styles tightly coupled to components.

💡 Hint

Think about when styles are mostly fixed and not tied to JavaScript logic.

SASS is great for large static sites with many global styles because it compiles to CSS before the site loads. CSS-in-JS shines when styles depend on JavaScript state or props.

🧠 Conceptual

intermediate

Why choose CSS-in-JS over SASS?

What is a key advantage of CSS-in-JS compared to SASS?

A It allows styles to change dynamically based on component state.

B It compiles styles into a single CSS file before runtime.

C It uses variables and nesting like SASS does.

D It requires no JavaScript to work.

💡 Hint

Consider how styles can respond to changes in your app.

CSS-in-JS lets you write styles that react to component state or props, enabling dynamic styling. SASS compiles static CSS before runtime.

📝 Syntax

advanced

Identify the CSS-in-JS syntax

Which code snippet correctly shows CSS-in-JS usage in a React component?

A button { background-color: blue; color: white; }

B $button-color: blue; .btn { background: $button-color; color: white; }

C const Button = styled.button`background: blue; color: white;`;

D <button style="background: blue; color: white;">Click</button>

💡 Hint

Look for template literals and styled components.

Option C uses the styled-components library syntax for CSS-in-JS in React. Option C is SASS syntax. Option C is plain CSS. Option C is inline HTML style.

❓ layout

advanced

How does SASS help with layout compared to CSS-in-JS?

Which statement about layout management with SASS vs CSS-in-JS is true?

A CSS-in-JS cannot use variables or mixins for layout.

B CSS-in-JS always produces smaller CSS files than SASS.

C SASS styles cannot be scoped to components.

D SASS allows reusable mixins and variables for consistent layout across many files.

💡 Hint

Think about how SASS features help reuse layout code.

SASS supports mixins and variables that help create consistent layouts reused across many files. CSS-in-JS can also use variables but mixins are a SASS feature. CSS-in-JS can scope styles to components, unlike global SASS styles.

❓ accessibility

expert

Accessibility considerations with CSS-in-JS vs SASS

Which accessibility practice is easier to enforce using CSS-in-JS compared to SASS?

A Dynamically adjusting focus styles based on component state.

B Writing semantic HTML tags.

C Using global CSS variables for color contrast.

D Adding ARIA attributes in CSS selectors.

💡 Hint

Think about how styles can respond to user interaction or state changes.

CSS-in-JS can dynamically change styles like focus outlines based on component state, improving accessibility. SASS compiles static CSS and cannot respond to runtime state changes. Semantic HTML and ARIA attributes are handled in HTML, not CSS.

Practice

1. Which situation is best suited for using SASS instead of CSS-in-JS?

easy

A. When you want to avoid using any CSS preprocessors or JavaScript.

B. When you want styles tightly coupled with JavaScript components for dynamic styling.

C. When you want to write inline styles directly inside HTML tags.

D. When you want to write styles in separate files with powerful CSS features like variables and nesting.

Solution

1. Step 1: Understand SASS purpose

   SASS is a CSS preprocessor that adds features like variables, nesting, and mixins to CSS, usually in separate style files.

2. Step 2: Compare with CSS-in-JS use case

   CSS-in-JS is best when styles need to be tightly integrated with JavaScript components, often for dynamic styling.

3. Final Answer:

   When you want to write styles in separate files with powerful CSS features like variables and nesting. -> Option D

4. Quick Check:

   SASS for separate powerful CSS files = C [OK]

Hint: SASS = separate style files; CSS-in-JS = styles inside JS [OK]

Common Mistakes:

• Confusing CSS-in-JS as better for all styling needs
• Thinking SASS is only for inline styles
• Assuming CSS-in-JS cannot use variables

2. Which of the following is the correct way to import a SASS file into another SASS file?

easy

A. @import 'styles.css';

B. @import 'variables.scss';

C. import 'variables.scss';

D. require('variables.scss');

Solution

1. Step 1: Recall SASS import syntax

   SASS uses @import 'filename.scss'; to include other SASS files.

2. Step 2: Check options for correct syntax

   @import 'variables.scss'; uses @import 'variables.scss'; which is correct. @import 'styles.css'; imports a CSS file, which is allowed but not typical for SASS partials. Options C and D use JavaScript syntax, which is incorrect in SASS.

3. Final Answer:

   @import 'variables.scss'; -> Option B

4. Quick Check:

   SASS import uses @import 'file.scss' = A [OK]

Hint: SASS imports use @import with quotes and .scss extension [OK]

Common Mistakes:

• Using JavaScript import syntax in SASS
• Importing CSS files instead of SASS partials
• Omitting quotes around file names

3. Given this SASS code:

$primary-color: blue;
.button {
  color: $primary-color;
  &:hover {
    color: darken($primary-color, 20%);
  }
}

What will be the color of the button text on hover in the compiled CSS?

medium

A. a darker shade of blue

B. blue

C. light blue

D. red

Solution

1. Step 1: Understand variable usage

   The variable $primary-color is set to blue and used as the button text color.

2. Step 2: Analyze hover color function

   The darken($primary-color, 20%) function makes the blue color 20% darker on hover.

3. Final Answer:

   a darker shade of blue -> Option A

4. Quick Check:

   darken(blue, 20%) = darker blue [OK]

Hint: darken() makes colors darker by given percent [OK]

Common Mistakes:

• Thinking hover color stays the same
• Confusing darken() with lighten()
• Assuming color changes to red

4. You wrote this CSS-in-JS code inside a React component:

const styles = {
  button: {
    color: 'blue',
    '&:hover': {
      color: 'darkblue'
    }
  }
};

But the hover style is not working. What is the likely problem?

medium

A. CSS-in-JS does not support pseudo-classes like :hover.

B. The color values must be variables, not strings.

C. The syntax for nested selectors in CSS-in-JS is incorrect; it should use a string key like ':hover' instead of '&:hover'.

D. The styles object must be converted to a CSS file manually.

Solution

1. Step 1: Understand CSS-in-JS pseudo-class syntax

   In many CSS-in-JS libraries, nested selectors use the key ':hover' without the ampersand (&).

2. Step 2: Identify syntax error

   The code uses '&:hover' which is valid in SASS but often incorrect in CSS-in-JS, causing hover styles to fail.

3. Final Answer:

   The syntax for nested selectors in CSS-in-JS is incorrect; it should use a string key like ':hover' instead of '&:hover'. -> Option C

4. Quick Check:

   CSS-in-JS pseudo-classes use ':hover' key, not '&:hover' [OK]

Hint: Use ':hover' key in CSS-in-JS, not '&:hover' [OK]

Common Mistakes:

• Using SASS syntax in CSS-in-JS
• Thinking CSS-in-JS can't do hover
• Forgetting to apply styles via className

5. You have a React project where components need dynamic styles based on props, but also want to share common styles across many components in separate files. Which approach best fits this need?

hard

A. Combine SASS for shared styles in separate files and CSS-in-JS for dynamic styles inside components.

B. Use only CSS-in-JS to keep all styles inside components with no external files.

C. Write all styles inline in HTML style attributes.

D. Use only SASS with separate .scss files and import them everywhere.

Solution

1. Step 1: Analyze project needs

   The project needs shared common styles in separate files and dynamic styles based on props inside components.

2. Step 2: Match approaches to needs

   SASS is great for shared styles in separate files. CSS-in-JS excels at dynamic styling inside components.

3. Step 3: Combine approaches

   Using both allows shared styles in SASS files and dynamic styles with CSS-in-JS, fitting both requirements.

4. Final Answer:

   Combine SASS for shared styles in separate files and CSS-in-JS for dynamic styles inside components. -> Option A

5. Quick Check:

   Shared styles + dynamic props = combine SASS + CSS-in-JS [OK]

Hint: Use SASS for shared, CSS-in-JS for dynamic styles [OK]

Common Mistakes:

• Trying to do all styling only with SASS or only CSS-in-JS
• Ignoring benefits of combining both
• Using inline styles for complex shared styles