Grid system mixin from scratch in SASS - Performance & Optimization

Performance: Grid system mixin from scratch

MEDIUM IMPACT

This affects page load speed and rendering performance by controlling how CSS grid layouts are generated and applied.

Creating a reusable grid layout with a Sass mixin

SASS

@mixin grid-good($columns) {
  display: grid;
  grid-template-columns: repeat(#{$columns}, 1fr);
}

Using only CSS grid properties avoids manual width calculations and lets the browser optimize layout.

📈 Performance GainSingle layout pass with minimal reflows and faster paint.

Creating a reusable grid layout with a Sass mixin

SASS

@mixin grid-bad($columns) {
  display: grid;
  grid-template-columns: repeat(#{$columns}, 1fr);
  > * {
    width: calc(100% / #{$columns});
  }
}

Forcing child widths with calc() inside the mixin causes redundant layout calculations and can trigger layout thrashing.

📉 Performance CostTriggers multiple reflows per child element due to width recalculations.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Manual width calc in mixin	N/A	Multiple reflows per child	Higher paint cost due to layout thrashing	[X] Bad
Pure CSS grid properties	N/A	Single reflow	Lower paint cost, optimized by browser	[OK] Good

Rendering Pipeline

The grid mixin sets CSS properties that the browser uses during style calculation and layout stages. Efficient grid definitions reduce layout complexity and repaint cost.

→Style Calculation

→Layout

→Paint

⚠️ BottleneckLayout stage is most expensive if widths are manually calculated causing reflows.

Core Web Vital Affected

LCP

This affects page load speed and rendering performance by controlling how CSS grid layouts are generated and applied.

Optimization Tips

1Avoid manual width calculations inside grid mixins to prevent layout thrashing.

2Use native CSS grid properties like grid-template-columns with repeat() for better performance.

3Test grid layouts in DevTools Performance panel to identify costly reflows and paints.

Performance Quiz - 3 Questions

What causes multiple reflows when using a grid mixin with manual width calculations?

A Applying display: grid only

B Setting child widths with calc() inside the mixin

C Using grid-template-columns with repeat()

D Using CSS variables for columns

DevTools: Performance

How to check: Record a performance profile while loading the page and interacting with the grid layout. Look for layout and paint events.

What to look for: Check for multiple layout recalculations and long layout durations indicating inefficient grid usage.

Practice

1. What is the main purpose of a grid system mixin in Sass?

easy

A. To create flexible column layouts with reusable code

B. To add colors to text elements

C. To write JavaScript functions inside Sass

D. To load external fonts automatically

Solution

1. Step 1: Understand the role of mixins in Sass

   Mixins let you reuse code blocks with parameters to customize styles.

2. Step 2: Identify what a grid system mixin does

   A grid system mixin helps create column layouts that adapt easily by changing parameters.

3. Final Answer:

   To create flexible column layouts with reusable code -> Option A

4. Quick Check:

   Grid mixin = flexible columns [OK]

Hint: Grid mixins simplify layout by reusing column code [OK]

Common Mistakes:

• Confusing mixins with variables
• Thinking mixins add colors only
• Assuming mixins run JavaScript

2. Which of the following is the correct way to define a simple grid mixin with columns and gap parameters in Sass?

easy

A. @mixin grid($columns, $gap) { display: flex; columns: $columns; gap: $gap; }

B. @mixin grid($columns, $gap) { display: block; grid-columns: $columns; grid-gap: $gap; }

C. @mixin grid($columns, $gap) { display: grid; grid-template-columns: repeat($columns, 1fr); gap: $gap; }

D. @mixin grid($columns, $gap) { display: grid; columns: $columns; gap: $gap; }

Solution

1. Step 1: Check the display property for grid layout

   Grid layouts require display: grid;, not flex or block.

2. Step 2: Verify grid-template-columns and gap syntax

   Using grid-template-columns: repeat($columns, 1fr); sets equal columns, and gap: $gap; sets spacing.

3. Final Answer:

   @mixin grid($columns, $gap) { display: grid; grid-template-columns: repeat($columns, 1fr); gap: $gap; } -> Option C

4. Quick Check:

   Grid needs display:grid and repeat() [OK]

Hint: Use display:grid and repeat() for columns [OK]

Common Mistakes:

• Using display:flex instead of grid
• Using incorrect property names like columns
• Missing repeat() function for columns

3. Given this Sass mixin and usage:

@mixin grid($cols, $gap) {
  display: grid;
  grid-template-columns: repeat($cols, 1fr);
  gap: $gap;
}

.container {
  @include grid(3, 2rem);
}

What CSS will be generated for .container?

medium

A. .container { display: grid; grid-template-columns: repeat(3, 1fr); gap: 2rem; }

B. .container { display: flex; columns: 3; gap: 2rem; }

C. .container { display: grid; grid-template-columns: 3fr; gap: 2rem; }

D. .container { display: block; grid-template-columns: repeat(3, 1fr); gap: 2rem; }

Solution

1. Step 1: Understand mixin parameters and usage

   The mixin sets grid display, columns with repeat, and gap using passed values 3 and 2rem.

2. Step 2: Translate Sass mixin to CSS output

   Including the mixin with (3, 2rem) generates CSS with display: grid;, grid-template-columns: repeat(3, 1fr);, and gap: 2rem;.

3. Final Answer:

   .container { display: grid; grid-template-columns: repeat(3, 1fr); gap: 2rem; } -> Option A

4. Quick Check:

   Mixin params = CSS properties [OK]

Hint: Repeat columns with 1fr for equal width [OK]

Common Mistakes:

• Confusing flex with grid display
• Writing grid-template-columns: 3fr instead of repeat()
• Using display:block by mistake

4. Identify the error in this Sass grid mixin:

@mixin grid($cols, $gap) {
  display: grid;
  grid-template-columns: repeat($cols 1fr);
  gap: $gap;
}

medium

A. gap property is invalid in grid layouts

B. Using display:flex instead of display:grid

C. Mixin parameters should be $columns and $gaps

D. Missing comma between $cols and 1fr in repeat() function

Solution

1. Step 1: Check syntax of repeat() function

   The repeat() function requires a comma between the number and the size, like repeat($cols, 1fr).

2. Step 2: Verify other properties

   Display is correctly set to grid, and gap is valid for grid layouts.

3. Final Answer:

   Missing comma between $cols and 1fr in repeat() function -> Option D

4. Quick Check:

   repeat() needs comma [OK]

Hint: Always put a comma inside repeat() between count and size [OK]

Common Mistakes:

• Omitting comma in repeat()
• Confusing display:flex with grid
• Thinking gap is invalid in grid

5. You want a responsive grid mixin that changes columns based on screen width. Which Sass code correctly adds a media query inside the mixin to set 2 columns on screens smaller than 600px and 4 columns otherwise?

hard

A. @mixin responsive-grid($gap) { display: grid; grid-template-columns: repeat(2, 1fr); gap: $gap; @media (min-width: 600px) { grid-template-columns: repeat(4, 1fr); } }

B. @mixin responsive-grid($gap) { display: grid; grid-template-columns: repeat(4, 1fr); gap: $gap; @media (max-width: 600px) { grid-template-columns: repeat(2, 1fr); } }

C. @mixin responsive-grid($gap) { display: flex; gap: $gap; @media (max-width: 600px) { flex-direction: column; } }

D. @mixin responsive-grid($gap) { display: grid; grid-template-columns: repeat(4, 1fr); gap: $gap; @media (min-width: 600px) { grid-template-columns: repeat(2, 1fr); } }

Solution

1. Step 1: Set default columns for large screens

   The mixin sets 4 columns by default using repeat(4, 1fr).

2. Step 2: Add media query for smaller screens

   Inside @media (max-width: 600px), columns change to 2 with repeat(2, 1fr).

3. Step 3: Confirm display and gap properties

   Display is grid and gap uses the parameter, which is correct.

4. Final Answer:

   @mixin responsive-grid($gap) { display: grid; grid-template-columns: repeat(4, 1fr); gap: $gap; @media (max-width: 600px) { grid-template-columns: repeat(2, 1fr); } } -> Option B

5. Quick Check:

   Default 4 cols, max-width 600px = 2 cols [OK]

Hint: Use max-width media query for smaller screens [OK]

Common Mistakes:

• Using min-width instead of max-width for small screens
• Setting flex display instead of grid
• Reversing column counts in media query