@if conditional logic in SASS - Mini Project: Build & Apply

@if Conditional Logic in Sass

📖 Scenario: You are designing a button style that changes color based on a theme variable. You want to use Sass @if conditional logic to set the button background color depending on whether the theme is 'dark' or 'light'.

🎯 Goal: Build a Sass stylesheet that uses @if conditional logic to set the button background color to #333 for dark theme and #eee for light theme.

📋 What You'll Learn

Create a Sass variable $theme with the value 'dark'.

Create a Sass variable $button-bg that uses @if to set background color based on $theme.

Use @if to check if $theme is 'dark' and assign #333 to $button-bg.

Use @else to assign #eee to $button-bg if $theme is not 'dark'.

Create a CSS rule for button that sets background-color to $button-bg.

💡 Why This Matters

🌍 Real World

Web developers often need to create themes or styles that change based on user preferences or settings. Using Sass @if conditional logic helps write clean, maintainable styles that adapt easily.

💼 Career

Knowing how to use Sass conditionals is valuable for front-end developers working on scalable CSS codebases, improving efficiency and reducing repetition.

1

Set up the theme variable

Create a Sass variable called $theme and set it to the string 'dark'.

SASS

# Create the $theme variable and set it to 'dark'
# Your code here

Hint

Use $theme: 'dark'; to create the variable.

2

Declare the button background variable

Create a Sass variable called $button-bg but do not assign a value yet.

SASS

$theme: 'dark';

// Declare $button-bg variable without value
# Your code here

Hint

Declare $button-bg with null to initialize it.

3

Use @if to set $button-bg based on $theme

Write an @if statement that checks if $theme equals 'dark'. If true, set $button-bg to #333. Use @else to set $button-bg to #eee if $theme is not 'dark'.

SASS

$theme: 'dark';
$button-bg: null;

// Use @if to set $button-bg based on $theme
# Your code here

Hint

Use @if $theme == 'dark' { $button-bg: #333; } and @else { $button-bg: #eee; }.

4

Create button style using $button-bg

Write a CSS rule for button that sets background-color to the Sass variable $button-bg.

SASS

$theme: 'dark';
$button-bg: null;

@if $theme == 'dark' {
  $button-bg: #333;
} @else {
  $button-bg: #eee;
}

// Create button style with background-color set to $button-bg
# Your code here

Hint

Use button { background-color: $button-bg; } to style the button.

Practice

1. What does the @if directive do in Sass?

easy

A. It defines a variable.

B. It loops through a list of items.

C. It imports other Sass files.

D. It applies styles only if a condition is true.

Solution

1. Step 1: Understand the purpose of @if

   The @if directive checks a condition and applies styles only when that condition is true.

2. Step 2: Compare with other options

   Looping is done with @for or @each, importing with @import, and variables are defined with $.

3. Final Answer:

   It applies styles only if a condition is true. -> Option D

4. Quick Check:

   @if = conditional style application [OK]

Hint: Remember: @if controls styles by conditions [OK]

Common Mistakes:

• Confusing @if with loops or imports
• Thinking @if defines variables
• Assuming @if always runs styles

2. Which of the following is the correct syntax for using @if in Sass?

easy

A. @if $color == red { color: red; }

B. @if ($color = red) { color: red; }

C. @if $color === red { color: red; }

D. @if $color => red { color: red; }

Solution

1. Step 1: Check the correct comparison operator

   Sass uses == to compare values in @if conditions, not =, ===, or =>.

2. Step 2: Verify syntax structure

   The correct syntax is @if $variable == value { ... } without parentheses around the condition.

3. Final Answer:

   @if $color == red { color: red; } -> Option A

4. Quick Check:

   Use == for comparison in @if [OK]

Hint: Use double equals (==) for conditions in @if [OK]

Common Mistakes:

• Using single equals (=) instead of double (==)
• Adding parentheses around condition
• Using JavaScript style === or =>

3. What will be the output CSS of this Sass code?

$theme: dark;

body {
  @if $theme == light {
    background: white;
    color: black;
  } @else if $theme == dark {
    background: black;
    color: white;
  } @else {
    background: gray;
    color: black;
  }
}

medium

A. body { background: black; color: white; }

B. body { background: white; color: black; }

C. body { background: gray; color: black; }

D. No output due to syntax error

Solution

1. Step 1: Check the value of $theme

   The variable $theme is set to dark.

2. Step 2: Evaluate the @if conditions

   The first condition $theme == light is false, so it skips to @else if $theme == dark, which is true. So it applies background: black; and color: white;.

3. Final Answer:

   body { background: black; color: white; } -> Option A

4. Quick Check:

   $theme = dark triggers @else if dark block [OK]

Hint: Match variable value to @if conditions carefully [OK]

Common Mistakes:

• Choosing first @if block without checking variable
• Ignoring @else if and @else blocks
• Assuming syntax error without checking carefully

4. Identify the error in this Sass code:

$size: 10px;

.box {
  @if $size > 5 {
    width: $size;
  } @else if $size < 5 {
    width: 5px;
  }
}

medium

A. Missing @else block for equal size case.

B. Units like px cannot be compared directly in @if.

C. Comparison operators like > and < are not allowed in @if.

D. Variable $size should be declared inside the block.

Solution

1. Step 1: Understand unit comparison in Sass

   Sass does not allow direct comparison of values with units like 10px > 5 in @if conditions.

2. Step 2: Check other options

   Comparison operators are allowed, @else block is optional, and variables can be declared outside blocks.

3. Final Answer:

   Units like px cannot be compared directly in @if. -> Option B

4. Quick Check:

   Cannot compare px units directly in @if [OK]

Hint: Avoid comparing units directly; use numbers or functions [OK]

Common Mistakes:

• Thinking > and < are invalid operators
• Assuming @else is mandatory
• Declaring variables only inside blocks

5. You want to set a button's background color based on a variable $status that can be 'success', 'warning', or 'error'. Which Sass code correctly uses @if conditional logic to apply green for success, yellow for warning, and red for error, with a default gray if none match?

hard

A. @if $status = success {
background: green;
} @else if $status == warning {
background: yellow;
} @else if $status == error {
background: red;
} @else {
background: gray;
}

B. @if $status = 'success' {
background: green;
} @else if $status = 'warning' {
background: yellow;
} @else if $status = 'error' {
background: red;
} @else {
background: gray;
}

C. @if $status == 'success' {
background: green;
} @else if $status == 'warning' {
background: yellow;
} @else if $status == 'error' {
background: red;
} @else {
background: gray;
}

D. @if $status === 'success' {
background: green;
} @else if $status === 'warning' {
background: yellow;
} @else if $status === 'error' {
background: red;
} @else {
background: gray;
}

Solution

1. Step 1: Check string comparison syntax

   In Sass, string values must be quoted and compared with ==, not = or ===.

2. Step 2: Verify the use of quotes around strings

   Options A and B miss quotes or use wrong operators; @if $status === 'success' { background: green; } @else if $status === 'warning' { background: yellow; } @else if $status === 'error' { background: red; } @else { background: gray; } uses === which is invalid in Sass.

3. Final Answer:

   @if $status == 'success' { background: green; } @else if $status == 'warning' { background: yellow; } @else if $status == 'error' { background: red; } @else { background: gray; } -> Option C

4. Quick Check:

   Use == and quotes for string comparison in @if [OK]

Hint: Compare strings with == and quotes in @if [OK]

Common Mistakes:

• Using single equals (=) instead of double (==)
• Omitting quotes around strings
• Using JavaScript style === operator