Boolean values and logic in SASS - Mini Project: Build & Apply

Boolean Values and Logic in Sass

📖 Scenario: You are creating a simple style sheet for a website that changes the background color of a button based on whether it is active or disabled. You will use boolean values and logic in Sass to control the button's style.

🎯 Goal: Build a Sass stylesheet that uses boolean variables and logical operations to set the background color of a button. The button should be green if active, gray if disabled, and blue otherwise.

📋 What You'll Learn

Create boolean variables for $is-active and $is-disabled with exact values.

Create a variable $default-color with the value #0000ff (blue).

Use an @if statement with boolean logic to set $button-color based on $is-active and $is-disabled.

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

💡 Why This Matters

🌍 Real World

Boolean values and logic in Sass help you create dynamic styles that change based on conditions, like button states or themes.

💼 Career

Understanding boolean logic in Sass is important for front-end developers to write clean, maintainable, and responsive stylesheets.

1

Set up boolean variables

Create two boolean variables in Sass: $is-active set to true and $is-disabled set to false.

SASS

# Create boolean variables $is-active and $is-disabled
# Your code here

Hint

Use true and false keywords in Sass to assign boolean values.

2

Add default color variable

Create a variable called $default-color and set it to the hex color #0000ff (blue).

SASS

$is-active: true;
$is-disabled: false;

# Create $default-color variable with value #0000ff
# Your code here

Hint

Use a hex color code to assign the default color.

3

Use boolean logic to set button color

Create a variable $button-color that uses @if logic: if $is-active is true, set $button-color to #00ff00 (green); else if $is-disabled is true, set it to #808080 (gray); otherwise, set it to $default-color.

SASS

$is-active: true;
$is-disabled: false;
$default-color: #0000ff;

# Use @if to set $button-color based on $is-active and $is-disabled
# Your code here

Hint

Use @if, @else if, and @else to check boolean variables and assign colors.

4

Apply button background color

Write a CSS rule for the button element that sets its background-color property to the $button-color variable.

SASS

$is-active: true;
$is-disabled: false;
$default-color: #0000ff;

@if $is-active == true {
  $button-color: #00ff00;
} @else if $is-disabled == true {
  $button-color: #808080;
} @else {
  $button-color: $default-color;
}

// Write CSS rule for button background-color
// Your code here

Hint

Use the button selector and set background-color to the variable.

Practice

1. In Sass, which of the following represents a Boolean value?

easy

A. 1

B. "true"

C. "false"

D. true

Solution

1. Step 1: Understand Sass Boolean values

   In Sass, Boolean values are the keywords true and false, not strings or numbers.

2. Step 2: Identify the correct Boolean

   true uses true as a keyword, which is the correct Boolean value in Sass.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Boolean values in Sass are true or false [OK]

Hint: Look for keywords true or false without quotes [OK]

Common Mistakes:

• Confusing strings "true" or "false" with Boolean values
• Using numbers like 1 or 0 as Booleans
• Thinking true/false must be quoted

2. Which of the following is the correct syntax to use a Boolean in an @if statement in Sass?

easy

A. @if $is-active == true { color: blue; }

B. @if $is-active = true { color: blue; }

C. @if $is-active === true { color: blue; }

D. @if $is-active != true { color: blue; }

Solution

1. Step 1: Check Sass comparison operator

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

2. Step 2: Identify correct syntax

   @if $is-active == true { color: blue; } uses == correctly to compare $is-active with true.

3. Final Answer:

   @if $is-active == true { color: blue; } -> Option A

4. Quick Check:

   Use double equals (==) for comparison in Sass [OK]

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

Common Mistakes:

• Using single equals (=) which assigns instead of compares
• Using triple equals (===) which is invalid in Sass
• Using != when checking for true

3. What color will the following Sass code output?

$dark-mode: false;

body {
  @if $dark-mode {
    background-color: black;
  } @else {
    background-color: white;
  }
}

medium

A. white

B. black

C. transparent

D. red

Solution

1. Step 1: Check the Boolean value of $dark-mode

   $dark-mode is set to false, so the @if condition is false.

2. Step 2: Follow the @else branch

   Since the condition is false, the code inside @else runs, setting background-color to white.

3. Final Answer:

   white -> Option A

4. Quick Check:

   False condition triggers @else block [OK]

Hint: False triggers @else styles, not @if [OK]

Common Mistakes:

• Assuming false runs the @if block
• Confusing true/false values
• Ignoring the @else block

4. Identify the error in this Sass code:

$is-visible: true

.container {
  @if $is-visible == true {
    display: block;
  } @else {
    display: none;
  }
}

medium

A. Incorrect use of @else block

B. Wrong comparison operator in @if

C. Missing semicolon after variable declaration

D. Variable name cannot start with $

Solution

1. Step 1: Check variable declaration syntax

   In Sass, variable declarations must end with a semicolon. Here, $is-visible: true is missing a semicolon.

2. Step 2: Verify other syntax

   The comparison operator == and @else block are correct. Variable names can start with $.

3. Final Answer:

   Missing semicolon after variable declaration -> Option C

4. Quick Check:

   Variable declarations need semicolons [OK]

Hint: Check for missing semicolons after variables [OK]

Common Mistakes:

• Forgetting semicolon after variable assignment
• Confusing = and == in @if
• Thinking @else is optional syntax

5. You want to apply a red border only if both $is-error and $is-active are true in Sass. Which code correctly uses Boolean logic to do this?

hard

A. @if $is-error & $is-active { border: 1px solid red; }

B. @if $is-error and $is-active { border: 1px solid red; }

C. @if $is-error && $is-active { border: 1px solid red; }

D. @if $is-error or $is-active { border: 1px solid red; }

Solution

1. Step 1: Understand Sass Boolean operators

   Sass uses the keyword and for logical AND, not symbols like && or &.

2. Step 2: Identify correct syntax

   @if $is-error and $is-active { border: 1px solid red; } correctly uses and to check if both variables are true before applying the border.

3. Final Answer:

   @if $is-error and $is-active { border: 1px solid red; } -> Option B

4. Quick Check:

   Use and for logical AND in Sass [OK]

Hint: Use 'and' keyword for AND logic in Sass [OK]

Common Mistakes:

• Using && or & which are invalid in Sass
• Using 'or' instead of 'and' for both true
• Confusing bitwise & with logical and