Why Variables in LESS

In CSS, if you are using the same value like color, font names, or any CSS values across multiple places or files, you have to use the same value repeatedly in multiple places.

For example, Let’s see declare a CSS file with blue as the primary color for headers.

.header1 {
  font-size:24px;
  color: blue;
}
.header3 {
  font-size:20px;
  color: blue;
}
.header3 {
   font-size:16px;
  color: blue;
}

In the above, the color: blue is repeatedly used in three selectors - header1,header2, and header3.

If you want to test or change the primary color to grey, You need to change it in three places.

To avoid this, LESS introduced the variables feature. Variables are declared and defined once, assigned the value to a variable and these can be used in multiple places or files.

variables provide reusability and maintainability for multiple modules

This enables Declare variable with value once and, reuse many times.

When you are designing styles or templates, All the variables are defined in a file, reuse this in files by import.

This provides variable values to be changed and the changes are reflected in multiple files wherever variables are being the user.

Variables in LESS are declared using at the rate of(@) symbol

Syntax

@variable-name: variabl-value

Variables are prefixed with the @ symbol and separated by colon with the value of the variable, the end of the line must be the semicolon(;) symbol.

The following are points to be noted for variable declaration

  • variable names contains hyphen(-) or underscore)(_) are interchangeable
  • Variable declaration and assignment must end with a semicolon
  • variable scope is nested only
  • can be used as a property names
  • variable values replaced by new values in the local scope
  • variable value contains font names color codes,

Let’s see how a variable is declared.

In the below example, the color-green variable is declared and assigned with the value green.

$color-green:green;

whenever blue color is required, We can reuse the value across multiple places

p{
background: $color-blue;
}

When the LESS compiler complied with the above codes, variables are replaced with their values in CSS snippets, The output is a CSS file with the below content as follows

p {
  background: blue;
}

color variables assigned other variables

Instead of assigning values, we can also assign other variables.

@font-color: red;

@link-color:@font-color;

h2{
color: @font-color
}
a{
color: @link-color
}

Generated CSS output after compilation

h2 {
  color: red;
}

a {
  color: red;
}

multiple font values assigned to a single variable

values can be color strings or numbers but also can be assigned with multiple values

$primary-font:("Sans",'Muli');


h2{
font-family: $primary-font
}

output is

h2 {
  font-family: "Sans", "Muli";
}

interpolation with CSS properties names

variables also can be used as HTML property names using interpolation syntax #{}

Enclose the variable with parenthesis prefixed with a hash symbol

Example

@primary-font:("Sans",'Muli');

$name: wrapper;
$attribute:border;

li.#{$name}{
#{$attribute}-radius:5px;
font-family:$primary-font;
}

compiled output css is

li.wrapper {
  border-radius: 5px;
  font-family: "Sans", "Muli";
}

Arithmetic operations on numbers not on strings

Arithmetic operations like division, addition, etc can be applied to variables of number types, operations on strings are not allowed

$height:1000px;
aside{
width :$height/3; // division operator
border-radius :ceil($height/3); // functions can be used
height: (1024px/3); // division
margin-right: 10px+4px/2px; // plus operation first, next division
font-size: 12px/4px; // Plain value, No athematic operation
}

Output is

aside {
  width: 333.3333333333px;
  border-radius: 333px;
  height: 341.3333333333px;
  margin-right: 12px;
  font-size: 12px/4px;
}

LESS constants

LESS modules define the predefined variable, called constants, these variables are not changed and act as constants For example, the math module has variables called constants which are not changeable, and can only be used in multiple places.

@use "sass: math" as math;
// this will give compilation failure
math.$e: 0;

The compilation gives a failure message

Error: Cannot modify the built-in variable.

LESS variables Scope

Scope is the usage of a variable at multiple places with limitations. It can be default or global scope. Variables are scoped in the nested level of their declaration.

Variables can be of two types.

  • Global variable is declared with! global keyword, ie global scope
  • local variables are declared under block-level ie declared inside parenthesis{} over written top variable value

Default scope variable usage

Global variables can be overwritten with the local variable of the same name Example

$primary-color: green;// global variable

.h1 {
  $primary-color: blue; // local variables
  background-color: $primary-color;
}

.p {
  background-color: $primary-color;
  }


.h1 {
  background-color: blue;
}

.p {
  background-color: green;
}

Global variable scope usage

$primary-color: green;// global variable

.h1 {
  $primary-color: blue !global; // local variables
  background-color: $primary-color;
}

.p {
  background-color: $primary-color;
  }

And output generated

.h1 {
  background-color: blue;
}

.p {
  background-color: blue;
}

Variable Advantages

  • Reusability
  • declare or update once, change in multiple places
  • uniform style design
  • clear separation of components when multiple teams are working