@each loop over maps in SASS - Browser Rendering Trace

Render Flow - @each loop over maps

Read SASS file

↓

Parse @each loop

↓

Extract map keys and values

↓

Iterate over each key-value pair

↓

Generate CSS rules for each pair

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Output compiled CSS

The SASS compiler reads the @each loop, extracts keys and values from the map, then repeats the inner code for each pair, generating CSS rules accordingly.

Render Steps - 3 Steps

Code Added:$colors: (red: #f00, green: #0f0, blue: #00f);

Before

[No boxes visible]

→

After

[No boxes visible]

Defines a map of color names to color codes; no visual change yet because no CSS applied.

🔧 Browser Action:Stores variable in SASS memory; no CSS output.

Code Sample

Creates three colored boxes: red, green, and blue, each styled using the @each loop over the colors map.

SASS

<div class="box red"></div>
<div class="box green"></div>
<div class="box blue"></div>

SASS

$colors: (red: #f00, green: #0f0, blue: #00f);

@each $name, $color in $colors {
  .box.#{$name} {
    background-color: $color;
    width: 5rem;
    height: 5rem;
    margin: 0.5rem;
    display: inline-block;
  }
}

Render Quiz - 3 Questions

After applying the @each loop in render_step 3, what do you see on the page?

A One large box with mixed colors

B Three colored boxes side by side: red, green, and blue

C No boxes visible

D Boxes stacked vertically without color

Common Confusions - 2 Topics

Why don't I see any boxes styled if I only define the map but forget the @each loop?

Defining a map only stores data in SASS; it does not create any CSS rules. The @each loop is needed to generate CSS for each map entry (see render_step 1 vs 3).

💡 Maps hold data; loops create visible styles.

Why does the class name need interpolation like .#{$name}?

Without interpolation, SASS treats the selector literally. Interpolation inserts the variable's value into the selector, creating unique class names (render_step 3).

💡 Use #{} to insert variables into selectors.

Property Reference

SASS Feature	Syntax	Purpose	Visual Effect	Common Use
@each loop	@each $key, $value in $map { ... }	Iterate over map entries	Generates repeated CSS rules	Create multiple classes or styles dynamically
Map	$map: (key1: value1, key2: value2);	Store key-value pairs	No direct visual effect	Hold related style values
Interpolation	.#{$name}	Insert variable into selector	Creates dynamic class names	Generate selectors from variables

Concept Snapshot

@each loop over maps lets you repeat CSS rules for each key-value pair. Use $map: (key: value, ...); to store pairs. Loop with @each $key, $value in $map { ... }. Use interpolation .#{$key} for dynamic class names. Generates multiple styled elements efficiently.

Practice

1. What does the @each loop do when used with a map in Sass?

easy

A. It creates a new map from the keys only.

B. It deletes all map entries after looping.

C. It repeats styles for each key-value pair in the map.

D. It converts the map into a list.

Solution

1. Step 1: Understand the purpose of @each with maps

   The @each loop iterates over each key-value pair in a map.

2. Step 2: Identify what happens during iteration

   For each pair, it repeats the block of styles or code inside the loop.

3. Final Answer:

   It repeats styles for each key-value pair in the map. -> Option C

4. Quick Check:

   @each loops over map pairs = repeats styles [OK]

Hint: Remember: @each repeats code for each map pair [OK]

Common Mistakes:

• Thinking @each deletes map entries
• Confusing map keys with list items
• Assuming it converts maps to lists

2. Which of the following is the correct syntax to loop over a map $colors with @each in Sass?

easy

A. @each $key $value in $colors { ... }

B. @each $colors in $key, $value { ... }

C. @each $value, $key in $colors { ... }

D. @each $key, $value in $colors { ... }

Solution

1. Step 1: Recall the correct @each syntax for maps

   The syntax requires two variables separated by a comma, then in, then the map name.

2. Step 2: Match the syntax to the options

   @each $key, $value in $colors { ... } correctly uses @each $key, $value in $colors. Others have wrong order or missing comma.

3. Final Answer:

   @each $key, $value in $colors { ... } -> Option D

4. Quick Check:

   Two variables separated by comma + in + map name [OK]

Hint: Use comma between key and value, then 'in' before map [OK]

Common Mistakes:

• Swapping key and value order
• Missing comma between variables
• Using wrong variable order or syntax

3. Given the Sass map and code:

$themes: (light: #fff, dark: #000); @each $name, $color in $themes { .#{$name}-theme { background: $color; } }

What CSS will this generate?

medium

A. .light-theme { background: #fff; } .dark-theme { background: #000; }

B. .light { background: #fff; } .dark { background: #000; }

C. .theme-light { background: #fff; } .theme-dark { background: #000; }

D. .light-theme { background: light; } .dark-theme { background: dark; }

Solution

1. Step 1: Understand the map and loop variables

   The map has keys light and dark with colors #fff and #000.

2. Step 2: Analyze the generated CSS selectors and properties

   The selector uses interpolation .#{$name}-theme producing .light-theme and .dark-theme. The background uses the color value.

3. Final Answer:

   .light-theme { background: #fff; } .dark-theme { background: #000; } -> Option A

4. Quick Check:

   Interpolation creates .light-theme and .dark-theme with correct colors [OK]

Hint: Interpolation with #{} creates dynamic class names [OK]

Common Mistakes:

• Forgetting interpolation syntax
• Using keys as colors instead of values
• Mixing up class name order

4. Identify the error in this Sass code:

$sizes: (small: 1rem, medium: 2rem); @each $size in $sizes { .btn-#{$size} { font-size: $size; } }

medium

A. Missing comma between key and value in @each loop.

B. Using only one variable for a map instead of two.

C. Incorrect interpolation syntax in class name.

D. Map keys and values are reversed.

Solution

1. Step 1: Check the @each loop variables

   The map has key-value pairs, so the loop needs two variables separated by a comma.

2. Step 2: Identify the problem with one variable

   The code uses only $size instead of $key, $value, so it cannot access both parts of the map.

3. Final Answer:

   Using only one variable for a map instead of two. -> Option B

4. Quick Check:

   Maps need two variables in @each loops [OK]

Hint: Use two variables for maps in @each loops [OK]

Common Mistakes:

• Using one variable for map iteration
• Forgetting comma between variables
• Misusing interpolation syntax

5. You have a Sass map:

$shadows: (none: 0 0 0 transparent, light: 0 1px 3px rgba(0,0,0,0.12), heavy: 0 4px 6px rgba(0,0,0,0.3));

Write a @each loop that creates classes .shadow-none, .shadow-light, and .shadow-heavy with the correct box-shadow property. Which code snippet is correct?

hard

A. @each $name, $shadow in $shadows { .shadow-#{$name} { box-shadow: $shadow; } }

B. @each $shadow, $name in $shadows { .shadow-#{$name} { box-shadow: $shadow; } }

C. @each $name in $shadows { .shadow-#{$name} { box-shadow: $name; } }

D. @each $name, $shadow in $shadows { .shadow-#{$shadow} { box-shadow: $name; } }

Solution

1. Step 1: Identify correct variable order for map iteration

   Maps use @each $key, $value in $map, so $name is key and $shadow is value.

2. Step 2: Check class name and property usage

   The class uses interpolation with the key $name, and the property uses the value $shadow.

3. Final Answer:

   @each $name, $shadow in $shadows { .shadow-#{$name} { box-shadow: $shadow; } } -> Option A

4. Quick Check:

   Key first, value second, use interpolation for class [OK]

Hint: Map loops: key first, value second, interpolate key for class [OK]

Common Mistakes:

• Swapping key and value variables
• Using only one variable for map
• Interpolating value instead of key in class name