@for loop (through vs to) in SASS - Browser Rendering Compared

Render Flow - @for loop (through vs to)

[Read @for loop syntax] -> [Determine loop range] -> [Iterate from start to end] -> [Generate CSS rules for each iteration] -> [Compile final CSS]

The Sass compiler reads the @for loop, decides the range based on 'through' or 'to', runs the loop for each number, and outputs CSS rules accordingly.

Render Steps - 3 Steps

Code Added:@for $i from 1 through 3 { .box#{$i} { width: 5rem * $i; height: 5rem; background-color: hsl(200, 70%, 50%); margin-bottom: 1rem; } }

Before

[ ]
[ ]
[ ]

→

After

[■■■■■_____]
[■■■■■■■■__]
[■■■■■■■■■■■]

Three boxes appear stacked vertically with widths increasing from 5rem to 15rem because 'through' includes 3.

🔧 Browser Action:Generates CSS for .box1, .box2, .box3; browser lays out boxes with specified widths and heights.

Code Sample

Three boxes with increasing widths are created; using 'through' includes the last number, 'to' excludes it.

SASS

<div class="box1"></div>
<div class="box2"></div>
<div class="box3"></div>

SASS

@for $i from 1 through 3 {
  .box#{$i} {
    width: 5rem * $i;
    height: 5rem;
    background-color: hsl(200, 70%, 50%);
    margin-bottom: 1rem;
  }
}

/* Change 'through' to 'to' changes loop range */

Render Quiz - 3 Questions

After applying the @for loop with 'through', how many boxes have visible width styles?

A Two boxes with increasing widths

B Three boxes all the same width

C Three boxes with increasing widths

D No boxes have width styles

Common Confusions - 2 Topics

Why does my loop skip the last number when I use 'to'?

'to' means the loop stops before the last number, so it excludes it. Use 'through' if you want to include the last number. See render_step 2 where changing 'through' to 'to' removes the last box.

💡 Remember: 'through' includes the end number; 'to' stops before it.

Why does my third box disappear when I use 'to'?

Because the loop only runs up to one less than the end number, no CSS is generated for the third box, so it has no size or color. See render_step 2 for the visual difference.

💡 Check how many iterations your loop runs to match your HTML elements.

Property Reference

Property	Value	Effect on Loop	Visual Result	Common Use
@for	from 1 through 3	Includes last number	Generates styles for 1, 2, 3	When you want to include the end number
@for	from 1 to 3	Excludes last number	Generates styles for 1, 2 only	When you want to exclude the end number
width	5rem * $i	N/A	Boxes grow wider each iteration	Create size variations
margin-bottom	1rem	N/A	Adds vertical spacing	Separate stacked elements visually

Concept Snapshot

@for loop in Sass runs a block multiple times. Use 'from X through Y' to include Y in the loop. Use 'from X to Y' to exclude Y. Loop variable can control styles like width. Changing 'through' vs 'to' changes how many times styles are generated.