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LESS WEB DEVELOPMENT ESSENTIALS
LESS WEB DEVELOPMENT ESSENTIALS

LESS WEB DEVELOPMENT ESSENTIALS: Use CSS preprocessing to streamline the development and maintenance of your web applications

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LESS WEB DEVELOPMENT ESSENTIALS

Chapter 2. Using Variables and Mixins

In this chapter, you will study Less in more detail, where you will learn more about variables and mixins. Variables in Less can be reused anywhere in the code. Although they are often defined in a single place, they can also be overwritten elsewhere in the code. They are used to define commonly used values that can be edited only once at a single place. Based on the Don't Repeat Yourself (DRY) principle, commonly used values will help you build websites that are easier to maintain. Mixins are used to set the properties of a class. They bundle tasks in a single line of code and are also reusable. You will learn how to create, use, and reuse them in your project and write better CSS without code duplications.

This chapter will cover the following topics:

  • Commenting on your code

  • Using variables

  • Escaping values

  • Using mixins

Comments


Comments make your code clear and readable for others. It is important that you are able to understand them clearly. That is why this chapter starts with some notes and examples of comments.

Tip

Don't be sparse with your comments when keeping the file size, download time, and performance in mind. In the process of compiling and minimizing your final CSS code, comments and other layout structures will be effectively removed. You can add comments for understanding and readability wherever needed.

In Less, you can add comments in the same way as you did while writing the CSS code. Comment lines are placed between /* */. Less also allows single-line comments that start with //.

Using Less, you will conserve these comments in the final style sheet apart from the single-line comments, which are not printed. Minimizers will remove these comments in your final compiled style sheet. An example of this can be seen in the following code:

/* comments by Bass
.mixins() { ~"this mixin is commented...

Variables


Variables in Less help you keep your files organized and easy to maintain. They allow you to specify widely-used values in a single place and then reuse them throughout your Less code. The properties of the final style sheet can be set with variables. So, imagine that you don't have to search for every declaration of a specific color or value in your style sheets any more. How does all of this work? Variables will start with @ and have a name. Examples of such variables include @color, @size, and @tree. To write the name, you are allowed to use any alphanumeric character, underscores, and dashes. This means that @this-is-variable-name-with-35-chars is a valid variable name.

Tip

Although alphanumeric characters, underscores, and dashes are used in variable names in this book, the specifications allow you to use any character, with a few exceptions. The specifications find their origin in the CSS grammar (which you can view at http://www.w3.org/TR/CSS21/grammar.html). Names starting...

Escaping values


Less is an extension of CSS. This means that Less gives an error when it comes across invalid CSS or evaluates a valid CSS during compilation. Some browsers define properties with an invalid CSS. Well-known examples will include something such as property: ms:somefunction(). Some of these rules can be replaced by vendor-specific rules. It is important to note that invalid property values won't get compiled in Less.

A new function, calc(), in CSS3 is a native CSS way of doing simple math as a replacement for a value of any length.

In both cases, Less won't give us the right value when we compile or import.

@aside-width: 80px;
.content {
width: calc(100% -  @aside-width)
}

The preceding code gets compiled into the following code:

.content {
  width: calc(20%);
}

From the preceding code, @aside-width: 80px; is the declaration of a variable with the name aside-width. This variable gets a value of 80 pixels. More information on variables will be covered in the following sections. However...

Mixins


Mixins play an important role in Less. You saw mixins in the first chapter when the rounded-corners example was discussed. Mixins take their naming from object-oriented programming. They look like functions in functional programming but in fact act like C macros. Mixins in Less allow you to embed all the properties of a class into another class by simply including the class name as one of its properties, as shown in the following code:

.mixin(){
  color: red;
      width: 300px;
  padding: 0 5px 10px 5px;
}
p{
.mixin();
}

The preceding code will get compiled into the following code:

p{
  color: red;
  width: 300px;
  padding: 0 5px 10px 5px;
}

In the final CSS code used on the website, every <p> paragraph tag will be styled with the properties defined in the mixin() function. The advantage will be that you can apply the same mixin on different classes. As seen in the rounded-corners example, you only have to declare the properties once.

Try opening less/mixins.less from the available...

Summary


In this chapter, you learned about variables and mixins. You have seen how defining variables and mixins at a single place will reduce your code and make it easy to maintain.

In the next chapter, you will learn more about mixins and how to nest and extend them. You will also read about the built-in functions of Less. Built-in functions can be used to manipulate values in mixins and other parts of your code.

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Description

Less is a CSS preprocessor that essentially improves the functionality of simple CSS with the addition of several features. The book begins by teaching you how Less facilitates the process of web development. You will quickly then move on to actually creating your first layout using Less and compiling your very first Less code. Next, you will learn about variables and mixins and how they will help in building robust CSS code. In addition, you'll learn how to keep your code clean and test it by using style guides. We will then move on to the concept of Bootstrapping and the strength of using Less with Twitter Bootstrap. Going one step further, you will be able to customize Twitter's Bootstrap 3 using Less. Finally, you will learn how to integrate Less into your WordPress themes and explore other web apps that use Less. By leveraging this powerful CSS preprocessor, you will be able to consistently produce amazing web applications while making CSS code development an enjoyable experience.

Who is this book for?

Every web designer who works with CSS and who wants to spend more time on real designing tasks should read this book. It doesn't matter if you are a beginner web designer or have used CSS for years; both will profit from reading this book and will learn how to utilize Less. We also recommend this book for teachers and students in modern web design and computer science. Less does not depend on a platform, language, or CMS. If you use CSS, you can and will benefit from Less.

What you will learn

  • Compile Less code into readable and maintainable CSS
  • Integrate Less into your own projects
  • Reuse your code to prevent code duplications
  • Reduce the development and maintenance time of your projects
  • Use variables and mixins to write reusable and portable code
  • Build a responsive grid with Less to create beautifully responsive site layouts
  • Customize Twitter s Bootstrap 3 with Less
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Length: 202 pages
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Table of Contents

6 Chapters
Improving Web Development with Less Chevron down icon Chevron up icon
Using Variables and Mixins Chevron down icon Chevron up icon
Nested Rules, Operations, and Built-in Functions Chevron down icon Chevron up icon
Avoid Reinventing the Wheel Chevron down icon Chevron up icon
Integrate Less in Your Own Projects Chevron down icon Chevron up icon
Bootstrap 3, WordPress, and Other Applications Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.5
(4 Ratings)
5 star 25%
4 star 25%
3 star 25%
2 star 25%
1 star 0%
Mike Ludemann Jul 18, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Alle wichtigen Information und mehr sind vorhanden.
Amazon Verified review Amazon
Abdul Mueid Jun 06, 2014
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
This book introduces Less as an extension to CSS3 and dives into it's feature set extensively, providing examples for each feature. The book also covers Less as used in Bootstrap and Wordpress and helps getting slightly hands-on, although that is not the purpose of this book and it is not covered in-depth.I should mention that this book is definitely not for learning about stylesheets from the ground up. A moderate know-how of CSS and a basic understanding of programming concepts (functions, variables, arrays, etc) is necessary in order to grasp many of the abstractions that Less provides.Overall, the book has met my expectations. I am giving 4 stars because this book could definitely improve in terms of examples and adopt Bootstrap as the go-to real world project to manipulate and demonstrate the capabilities of Less.
Amazon Verified review Amazon
Antonis Ntoumanis May 28, 2014
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
I can code basic things on LESS and CSS. So I wanted to learn more especially integrating with bootstrap. While reading the book (kindle version) I found my self often confused because of some assumptions the writer made. That doesn't mean that it is a bad book. A lot of information is there, but what I want when I read something is some inspiration, something that this book didn't deliver. I think its more of writing style issue.
Amazon Verified review Amazon
Josh Archer May 24, 2015
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
The book has some fantastic points and covers LESS well. Unfortunately, they hired a very poor editor. Misspelled words (MS word could fix this for them?!?!), sloppy code with massive/obvious spacing and indentation errors, and poor wording drags the quality of the book down. This seems like a lazy money grab.
Amazon Verified review Amazon
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