Control directives and expressions are used in SASS to include styles only under certain defined conditions.
As a feature, they’re quite advanced and are mainly useful in mixins. Common directives include @if
, @else
, @for
and @while
.
@if and @else
The @if
and @else
directives are similar to if
and else
statements in JavaScript.
@if
takes an expression and executes the styles contained within its block — if the evaluation is not false (or null).
@else
will then be checked, if the previous @if
evaluated to false.
For example:
@mixin heading($size) {
@if $size == large {
font-size: 4rem;
}
@else if $size == medium{
font-size: 3rem;
}
@else if $size == small {
font-size: 2rem;
}
@else {
font-size: 1rem;
}
}
.h1 {
@include heading(large);
}
.h6 {
@include heading(small);
}
Here, we are using a heading mixin which accepts $size
as an argument. We can have a different size for each of our headings depending on which value we pass to the mixin.
@for
You can use the @for
directive to execute a group of statements a specified number of times. Effectively this is a loop.
It has two variations. The first uses the through
keyword, it’ll execute the statements from start to end, inclusive.
An example using through
:
@for $i from 1 through 5 {
.list-#{$i} {
width: 2px * $i;
}
}
This will produce the following CSS output:
.list-1 {
width: 2px;
}
.list-2 {
width: 4px;
}
.list-3 {
width: 6px;
}
.list-4 {
width: 8px;
}
.list-5 {
width: 10px;
}
If we replace the through
keyword with to
, it makes the loop exclusive. The difference being that it won’t execute when the variable is equal to end.
An example using to
:
@for $i from 1 to 5 {
.list-#{$i} {
width: 2px * $i;
}
}
This produces the following CSS:
.list-1 {
width: 2px;
}
.list-2 {
width: 4px;
}
.list-3 {
width: 6px;
}
.list-4 {
width: 8px;
}
@while
We could instead implement the above code using the @while
directive. As its name implies, it will continue to output CSS produced by the statements while the condition returns true.
The syntax is as follows:
$i: 1;
@while $i < 6 {
.list-#{$i} {
width: 2px * $i;
}
$i: $i + 1;
}
The output is identical, so you could opt for your personal preference based on the syntax.
In the next article, we’ll look at SASS interpolation.
Conclusion
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