Flex grow and shrink in Tailwind - Performance & Optimization

Performance: Flex grow and shrink

MEDIUM IMPACT

This affects how flex items resize within a container, impacting layout recalculations and paint times during resizing or dynamic content changes.

Making flex items resize smoothly without causing layout thrashing

Tailwind

<div class="flex">
  <div class="flex-grow flex-shrink basis-64">Flexible base size item</div>
  <div class="flex-grow flex-shrink">Flexible item</div>
</div>

Using flex-basis with grow and shrink allows smoother resizing with fewer layout recalculations and stable layout.

📈 Performance GainSingle reflow on resize, reducing CLS and improving user experience.

Making flex items resize smoothly without causing layout thrashing

Tailwind

<div class="flex">
  <div class="flex-grow-0 flex-shrink-0 w-64">Fixed width item</div>
  <div class="flex-grow flex-shrink">Flexible item</div>
</div>

Using fixed width on one item with grow and shrink on another causes frequent reflows and layout shifts when container size changes.

📉 Performance CostTriggers multiple reflows on container resize, causing noticeable layout shifts (high CLS).

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Fixed width with flex-grow/shrink mix	Low	Multiple on resize	High due to layout shifts	[X] Bad
Consistent flex-basis with grow and shrink	Low	Single on resize	Low, smooth resizing	[OK] Good

Rendering Pipeline

Flex grow and shrink affect the Layout stage by recalculating sizes of flex items when container size changes. This triggers Paint and Composite stages to update visuals.

→Layout

→Paint

→Composite

⚠️ BottleneckLayout recalculation is most expensive due to resizing flex items dynamically.

Core Web Vital Affected

CLS

This affects how flex items resize within a container, impacting layout recalculations and paint times during resizing or dynamic content changes.

Optimization Tips

1Avoid mixing fixed widths with flex-grow and flex-shrink on sibling items.

2Use flex-basis to set a base size for flex items to stabilize layout.

3Test resizing behavior to ensure minimal layout recalculations and shifts.

Performance Quiz - 3 Questions

What is the main performance cost of using flex-grow and flex-shrink improperly?

A More network requests for CSS files

B Increased JavaScript execution time

C Frequent layout recalculations causing reflows

D Slower image decoding

DevTools: Performance

How to check: Record a performance profile while resizing the flex container or changing window size. Look for Layout and Recalculate Style events.

What to look for: Multiple Layout events indicate costly reflows; fewer Layout events mean better performance with flex grow/shrink usage.

Practice

1. What does the Tailwind class flex-grow-0 do to a flex item?

easy

A. Prevents the item from growing to fill extra space

B. Makes the item grow to fill all extra space

C. Prevents the item from shrinking when space is tight

D. Makes the item shrink faster than others

Solution

1. Step 1: Understand flex-grow property

   The flex-grow property controls how much a flex item can grow relative to others when extra space is available.

2. Step 2: Interpret the class flex-grow-0

   The class flex-grow-0 sets flex-grow to 0, meaning the item will not grow to fill extra space.

3. Final Answer:

   Prevents the item from growing to fill extra space -> Option A

4. Quick Check:

   flex-grow-0 means no growth [OK]

Hint: flex-grow-0 means no growth, flex-grow-1 means grow [OK]

Common Mistakes:

• Confusing grow with shrink
• Thinking flex-grow-0 allows growth
• Mixing flex-grow with flex-shrink

2. Which Tailwind class correctly prevents a flex item from shrinking?

easy

A. flex-grow-1

B. flex-grow-0

C. flex-shrink-1

D. flex-shrink-0

Solution

1. Step 1: Understand flex-shrink property

   The flex-shrink property controls how much a flex item shrinks when space is limited.

2. Step 2: Identify the class that disables shrinking

   The class flex-shrink-0 sets flex-shrink to 0, preventing the item from shrinking.

3. Final Answer:

   flex-shrink-0 -> Option D

4. Quick Check:

   flex-shrink-0 means no shrinking [OK]

Hint: Use flex-shrink-0 to stop shrinking, flex-shrink-1 to allow [OK]

Common Mistakes:

• Choosing flex-grow classes instead of flex-shrink
• Assuming flex-shrink-1 prevents shrinking
• Mixing grow and shrink properties

3. Given this HTML snippet:

<div class="flex w-64">
  <div class="flex-grow-0 w-16 bg-blue-500">A</div>
  <div class="flex-grow w-32 bg-red-500">B</div>
</div>

What will happen to the widths of the two divs inside the flex container?

medium

A. A shrinks, B stays fixed at 32 width

B. A stays 16 width, B grows to fill remaining space

C. Both A and B grow equally to fill space

D. A grows, B shrinks to 16 width

Solution

1. Step 1: Analyze flex-grow classes

   Div A has flex-grow-0 so it won't grow beyond its width 16. Div B has flex-grow (equivalent to flex-grow-1) so it will grow to fill leftover space.

2. Step 2: Understand container width and item widths

   The container is 64 width. A uses 16 width fixed, B starts at 32 but grows to fill remaining space (64 - 16 = 48 or more if allowed).

3. Final Answer:

   A stays 16 width, B grows to fill remaining space -> Option B

4. Quick Check:

   flex-grow-0 no grow, flex-grow fills space [OK]

Hint: flex-grow-0 fixes size, flex-grow fills leftover space [OK]

Common Mistakes:

• Assuming flex-grow-0 items grow
• Thinking both grow equally without flex-grow class
• Ignoring container width limits

4. You have this code:

<div class="flex w-40">
  <div class="flex-shrink-0 w-24 bg-green-400">X</div>
  <div class="flex-shrink w-24 bg-yellow-400">Y</div>
</div>

But the second div overflows the container. What is the problem?

medium

A. flex-shrink on second div prevents shrinking, causing overflow

B. w-24 is too small for both divs, causing overflow

C. flex-shrink-0 on first div prevents it from shrinking, causing overflow

D. Missing flex-grow classes causes overflow

Solution

1. Step 1: Check widths and container size

   Container width is 40. Both divs have width 24, total 48, which is more than container.

2. Step 2: Analyze flex-shrink classes

   First div has flex-shrink-0, so it cannot shrink below 24. Second div has default shrink, so it tries to shrink but can't reduce enough to fit container.

3. Final Answer:

   flex-shrink-0 on first div prevents it from shrinking, causing overflow -> Option C

4. Quick Check:

   flex-shrink-0 stops shrinking, causes overflow [OK]

Hint: flex-shrink-0 stops shrinking, watch container overflow [OK]

Common Mistakes:

• Thinking flex-shrink on second div causes overflow
• Ignoring container width limits
• Assuming flex-grow affects shrinking

5. You want three flex items inside a container to share leftover space proportionally: the first twice as much as the second, and the third does not grow. Which Tailwind classes should you use?

hard

A. First: flex-grow-2, Second: flex-grow-1, Third: flex-grow-0

B. First: flex-grow, Second: flex-grow-2, Third: flex-grow-0

C. First: flex-grow-1, Second: flex-grow-2, Third: flex-grow-0

D. First: flex-grow-0, Second: flex-grow-1, Third: flex-grow-2

Solution

1. Step 1: Understand proportional growth with flex-grow

   Flex-grow values determine how leftover space is divided. A value of 2 means twice the space compared to 1.

2. Step 2: Assign classes to match proportions

   First item needs flex-grow-2, second flex-grow-1, third flex-grow-0 to not grow.

3. Final Answer:

   First: flex-grow-2, Second: flex-grow-1, Third: flex-grow-0 -> Option A

4. Quick Check:

   flex-grow values set proportional growth [OK]

Hint: Use flex-grow numbers to set proportional growth [OK]

Common Mistakes:

• Using wrong grow numbers or order
• Assigning flex-grow-0 to growing items
• Confusing grow with shrink classes