What does a CSS Preprocessor Do?

As we know CSS doesn't have the properties and functionalities that a programming language like C++, Java, etc. have, so many beginner developers find it difficult to use. It's feasible for a coding novice to feel the need to use conditional statements or a loop to generate some dynamic styles in using the raw CSS, but this is just not doable without a little assistance from some other tools. The CSS Preprocessors steps in to rescue the day at this point!

We use a specific CSS compiler to write the dynamic styling code, and then the code is compiled using the CSS preprocessors. The preprocessor then produces a regular CSS file, which the primary HTML document uses for its reference.

You can also program in standard CSS when using any CSS Preprocessor, just as you would if the CSS preprocessor weren't there. The good news is that you have alternatives at your side like SASS, it includes special style guidelines, like if you'd prefer to write code without braces {}, you can do it using SASS.

Of course, CSS Preprocessors also provide other functionalities. Although, the functionality provided by different preprocessors is quite similar to one another with just minor syntactic differences.

Syntax

A simple example of SASS and SCSS syntax is shown below ( SASS and SCSS are types of CSS preprocessors, which we will thoroughly discussed in the article further). Two variables, $first-color, and $bg-color are simply declared in the code and applied to the body HTML element.

The identical code in SASS syntax:

Both provide the same CSS when compiled:

The SCSS syntax is quite compliant with the conventional CSS syntax, while the SASS syntax is easier to write and less prone to errors.

What Is a CSS Preprocessor?

Preprocessors for CSS are scripting languages that enhance CSS's built-in features. We can use variables, nesting, conditional statements, loops, functions, and mathematical operations to add logical functionalities to our CSS code. CSS preprocessors also provide DRY(Don't Repeat Yourself) functionality, lower the number of mistakes, and provide reusable code snippets and backward compatibility.

Each CSS preprocessor provides a unique syntax that is translated into standard CSS to enable client-side rendering by browsers. There are other smaller CSS preprocessors, but LESS, SASS, SCSS, and Stylus are currently the four most widely used and reliable ones. Each of them has its ecosystem (tools, frameworks, and libraries) as well as certain advanced capabilities that are exclusive to them.

What Is the Difference Between Popular Preprocessors?

Even though SASS, SCSS, LESS, and Stylus share roughly 80% of the same functionalities, each CSS preprocessor has its method of carrying out the same operation. The remaining 20% is made up of minute variations in advanced usage. You can use variables, nesting, mixins, extends, loops & if/else, and imports. All four can provide you an edge over simple CSS since they all allow you to abstract important design aspects, use logic, and write less code.

SASS

SASS is Syntactically Awesome Style Sheets. It was built using Ruby, and it includes the Gumby and Foundation frameworks. Popular mixin libraries like Compass and Bourbon are also available in SASS. SASS differs from LESS and Stylus in a few ways, like SASS includes @extend , @media, and @content.

• You can transfer a group of CSS properties from one selector to another with @extend.
• You can target various screen sizes by using media queries inside nesting using the @media feature.
• A block of styles can be passed to the mixin through @content and placed inside the styles that the mixin has included.

SCSS

SCSS is Sassy Cascading Style Sheets. It is like SASS but is more comparable to standard CSS. Since SCSS is entirely compatible with CSS, you can import standard CSS into a SCSS file and it will function right away. This is excellent if you're copying some code from standard CSS since it's clear and well-written and you don't need to spend time rewriting everything.

LESS

LESS is Leaner Style Sheets. LESS operates in the browser's Node Javascript environment. LESS and other CSS preprocessors vary primarily as LESS permits real-time compilation through less.js in the browser. When constructing a mixin in SASS or Stylus, we first build a collection of CSS declarations, but in LESS, we embed the mixin inside a property of the class.

Stylus

Stylus, which is based on node.js, effectively removes all the unnecessary characters that clutter your CSS. You have flexibility with Stylus's syntax; you can eliminate braces {}, semicolons ;, and even colons :. Conditionals and strong in-language functions are popular features of Stylus.

Top Reasons to Use a CSS Preprocessor

1. DRY CSS, also known as Don't Repeat Yourself. Thanks to CSS preprocessors, you can reuse styles without having to write the same code repeatedly.
2. It improves the maintainability of your code. For instance, you can state your brand's colors in one location using a variable name and it will be easier for you to modify the color name at once for all elements.
3. It will improve the organization of your CSS code. SASS and LESS support nesting definitions, which keeps everything in order. We can see how monotonous the previous method was once we start creating our CSS definitions using nesting.
4. It is time-saving and fun. When you are not needed to write the same code repeatedly, you will be amazed at how much time you can save and how fun it will be to code.

Cons of Using a CSS Preprocessor

1. The code is tougher to debug. Finding the source of the problem could take longer because we're using duplicate code.
2. More time for complications. Since the browser cannot comprehend this more complex form of CSS, it must be converted into standard CSS before the style can be shown.
3. CSS Preprocessors may create the standard CSS files that are very large, but the source files will be shorter. This can make it take longer for a request to be fulfilled.

CSS Preprocessor Features

The main features of a CSS Preprocessor are as follows:

Variables

You can define variables in your CSS to reuse data many times:

Nesting

CSS Preprocessor enable the feature to construct hierarchical CSS components (nested elements):

Here, all the list (<li>) elements will have a margin of 10px that are inside the un-ordered list (<ul>) element in the HTML document.

Mixins

With the use of mixins, you can include a prewritten set of CSS rules into the style of any CSS element. This is a great way to reduce repetitive code.

Here, we have a mixin that enables us to pass an argument that will be utilized to set the object's width within the element having id mydiv.

Extends

You can extend any element to share its whole array of CSS rules with another element of your choice. Because elements may extend their entire style to other components, the term extend was created.

Here, the element with the id #another-div inherits all of the styling of the class .app-div using @extend.

If/Else Statements

Preprocessors enable your style to dynamically change based on particular conditionals using @if, @else if , and @else.

Here, in the .app-div class, we call the setcolor mixin, which contains the conditions. Depending on the direction we set the color of our border, if $dir is right, we set the border-left-color: $color (here, $color: black), and so on.

Color Functions

CSS preprocessors support a large range of built-in functions for dynamically changing the color. Some of these functions are listed below:

Loops

Using the loop syntax in a preprocessor makes it feasible to iterate over the CSS code:

By this loop, divs with class names .app-div1 will have increasingly lighter yellow backgrounds till .app-div100.

Imports

Importing other stylesheets allows you to quickly integrate numerous files into one without having to write any new code.

Math

Preprocessors eliminate the requirement for the calc() function from the standard CSS by allowing arithmetic to be put anywhere within a CSS rule.