Function definition with @function in SASS - Mini Project: Build & Apply

Create a Sass Function with @function

📖 Scenario: You are styling a website and want to create a reusable Sass function that calculates the double of a number. This will help you keep your styles consistent and easy to update.

🎯 Goal: Build a Sass function named double that takes one number as input and returns its double. Then use this function to set the width of a container.

📋 What You'll Learn

Create a Sass function named double using @function

The function must take one parameter named $number

The function must return $number * 2

Use the double function to set the width of a .container class to double 100px

💡 Why This Matters

🌍 Real World

Sass functions help you write reusable and maintainable styles by calculating values dynamically.

💼 Career

Knowing how to write Sass functions is useful for front-end developers to create scalable CSS codebases.

1

Create the Sass function skeleton

Write a Sass function named double using @function that takes one parameter called $number. Do not add the return value yet.

SASS

@function double($number) {
  // Your code here
}

Hint

Use @function followed by the function name and parameters in parentheses. Inside, use @return to send back a value.

2

Add the return statement to double the number

Modify the double function to return the value of $number * 2 instead of null.

SASS

@function double($number) {
  // Change the return value to double $number
}

Hint

Replace null with $number * 2 in the @return statement.

3

Use the function to set container width

Create a CSS class called .container and set its width property to the result of calling the double function with 100px as the argument.

SASS

@function double($number) {
  @return $number * 2;
}

.container {
  // Set width using double(100px)
}

Hint

Use the function by writing double(100px) as the value for width.

4

Add a comment explaining the function

Add a comment above the @function double line explaining that this function doubles a number.

SASS

// Your comment here
@function double($number) {
  @return $number * 2;
}

.container {
  width: double(100px);
}

Hint

Write a single-line comment starting with // describing the function.

Practice

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

easy

A. It defines reusable code blocks that return values.

B. It imports external CSS files.

C. It creates variables for colors.

D. It applies styles to HTML elements.

Solution

1. Step 1: Understand the purpose of @function

   The @function directive in Sass is used to create reusable blocks of code that can return a value.

2. Step 2: Compare with other options

   Options A, B, and D describe other Sass or CSS features, but only C correctly describes @function.

3. Final Answer:

   It defines reusable code blocks that return values. -> Option A

4. Quick Check:

   @function creates reusable code blocks [OK]

Hint: Remember: @function returns values, not styles directly [OK]

Common Mistakes:

• Confusing @function with @mixin
• Thinking @function applies styles
• Mixing up @function with variable declaration

2. Which of the following is the correct syntax to define a function named double that returns twice the input $n in Sass?

easy

A. @function double($n) { @return $n * 2; }

B. @function double($n) { return $n * 2; }

C. function double($n) { @return $n * 2; }

D. @mixin double($n) { @return $n * 2; }

Solution

1. Step 1: Check the function declaration syntax

   In Sass, functions start with @function, followed by the name and parameters in parentheses.

2. Step 2: Verify the return statement

   The correct way to return a value is using @return, not just return.

3. Final Answer:

   @function double($n) { @return $n * 2; } -> Option A

4. Quick Check:

   Use @function and @return for Sass functions [OK]

Hint: Use @function and @return keywords exactly [OK]

Common Mistakes:

• Using 'return' instead of '@return'
• Omitting the @ in @function
• Confusing @function with @mixin

3. Given the Sass function:

@function add($a, $b) { @return $a + $b; }

What will be the output of this Sass code?

.result { width: add(10px, 5px); }

medium

A. .result { width: 10px 5px; }

B. .result { width: 15px; }

C. Syntax error

D. .result { width: add(10px, 5px); }

Solution

1. Step 1: Understand the function behavior

   The function add takes two values and returns their sum using @return $a + $b;.

2. Step 2: Apply the function in the style

   Calling add(10px, 5px) returns 15px, so the CSS becomes .result { width: 15px; }.

3. Final Answer:

   .result { width: 15px; } -> Option B

4. Quick Check:

   Function returns sum, so width is 15px [OK]

Hint: Functions return values, so output replaces function call [OK]

Common Mistakes:

• Expecting function name to appear in output
• Confusing list output with addition
• Thinking it causes syntax error

4. Identify the error in this Sass function:

@function multiply($x, $y) { return $x * $y; }

medium

A. Parameters must be strings

B. Function name is invalid

C. Missing @ before return keyword

D. Function cannot have two parameters

Solution

1. Step 1: Check the return statement syntax

   In Sass functions, the return keyword must be @return, not just return.

2. Step 2: Verify other parts

   The function name and parameters are valid, and multiple parameters are allowed.

3. Final Answer:

   Missing @ before return keyword -> Option C

4. Quick Check:

   Use @return, not return [OK]

Hint: Always use @return in Sass functions [OK]

Common Mistakes:

• Using 'return' without @
• Thinking parameters must be strings
• Believing function names can't have multiple parameters

5. You want to create a Sass function shade-color that darkens a color by a percentage. Which of these function definitions correctly uses @function and @return to achieve this?

A) @function shade-color($color, $percent) { @return darken($color, $percent); }
B) @function shade-color($color, $percent) { return darken($color, $percent); }
C) @mixin shade-color($color, $percent) { @return darken($color, $percent); }
D) @function shade-color($color, $percent) { darken($color, $percent); }

hard

A. @function shade-color($color, $percent) { darken($color, $percent); }

B. @function shade-color($color, $percent) { return darken($color, $percent); }

C. @mixin shade-color($color, $percent) { @return darken($color, $percent); }

D. @function shade-color($color, $percent) { @return darken($color, $percent); }

Solution

1. Step 1: Confirm correct function syntax

   The function must start with @function and use @return to send back the value.

2. Step 2: Check each option

   @function shade-color($color, $percent) { @return darken($color, $percent); } uses @function and @return correctly. @function shade-color($color, $percent) { return darken($color, $percent); } uses return without @, which is invalid. @mixin shade-color($color, $percent) { @return darken($color, $percent); } uses @mixin instead of @function. @function shade-color($color, $percent) { darken($color, $percent); } lacks a return statement.

3. Final Answer:

   @function shade-color($color, $percent) { @return darken($color, $percent); } -> Option D

4. Quick Check:

   Use @function with @return for value-returning functions [OK]

Hint: Functions need @return; mixins do not return values [OK]

Common Mistakes:

• Using return without @
• Confusing mixin with function
• Omitting @return statement