Less.js Mixins Mixin Guards

LESS is a Leaner Style Sheets, a simple CSS pre-processor that facilitates the creation of manageable, customizable, and reusable style sheets for websites. It is a dynamic style sheet language that enhances the working power of CSS. LESS supports cross-browser compatibility. CSS pre-processor is a scripting language that improves CSS and gets compiled into regular CSS syntax so that the web browser can use it. It is also a backward-compatible language extension for CSS that provides functionalities like variables, functions, mixins, and operations that enable us to build dynamic CSS.

Mixins in less: Mixins in LESS, along with understanding their implementation & usage through the example. A CSS preprocessor is a program that generates the CSS code by using the defined preprocessor ruleset & facilitates reducing the overall complexity of CSS code. LESS is a CSS preprocessor that is a CSS backward-compatible language extension. Mixins in LESS, are a way to include a bunch of CSS properties from one ruleset to another i.e multiple times in the same file.

Mixin Guards: If you want to match simple values or a number of arguments on expressions, then you can use guards. It is associated with a mixin declaration and includes a condition that is attached to a mixin. Each mixin will have one or more guards which are separated by a comma; a guard must be enclosed within parentheses. LESS uses guarded mixins instead of if/else statements and performs calculations to specify matched mixin.

Different types of mixin guards:

• Guard Comparison Operators

Parameter: You can use the comparison operator (=) to compare numbers, strings, identifiers, etc. There are some comparison operators usable in guards: >, >=, =, =<. Additionally, the keyword true is the only truthy value, making these two mixins equivalent.

• Guard Logical Operators:

Parameter: You can use keywords to work around logical operators with guards.

• Type Checking Functions: It contains the built-in functions to determine the value types for matching mixins.

Mixin guards:

Syntax:

.p-style(@size) when (@size<=50){
   font-size: @size;
   color:green;   
}

Example 1: The following example, demonstrates the use of mixin guards.

style.less: Create a less file.

Now, to compile the above LESS code to CSS code, run the following command:

lessc style.less style.css

The compiled CSS file comes to be: 

style.css

Output:

 

Example 2: The following example demonstrates the use of mixin guards.

style.less: Creates the less file

Now, to compile the above LESS code to CSS code, run the following command:

lessc style.less style.css

The compiled CSS file comes to be: 

style.css

Output:

 

Reference: https://lesscss.org/features/#mixins-feature-mixin-guards-feature