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Less vs Sly

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When comparing Less vs Sly, the Slant community recommends Less for most people. In the question“What are the best CSS preprocessors/postprocessors?” Less is ranked 3rd while Sly is ranked 8th. The most important reason people chose Less is:

Because Less has a lightweight feature set, is syntactically similar to CSS and can be run client side with file conversion on a page reload, it is easy to pick up by anyone familiar with CSS & the very basics of JS. Also, Less has detailed and well-organized documentation, GUI apps that can watch and compile code for you and a huge, active and helpful community.

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Common Questions

What are the best CSS preprocessors/postprocessors?

Pros

Pro
Easy to learn

Also, Less has detailed and well-organized documentation, GUI apps that can watch and compile code for you and a huge, active and helpful community.

Pro
Familiar CSS style syntax

The LESS syntax is essentially the same as CSS with extensions for dynamic behavior such as variables, mixins, operations and functions.

Variables:

@color: #4D926F;

#header {
  color: @color;
}
h2 {
  color: @color;
}

Mixins:

.rounded-corners (@radius: 5px) {
  -webkit-border-radius: @radius;
  -moz-border-radius: @radius;
  -ms-border-radius: @radius;
  -o-border-radius: @radius;
  border-radius: @radius;
}

#header {
  .rounded-corners;
}
#footer {
  .rounded-corners(10px);
}

Nested Rules:

#header {
  h1 {
    font-size: 26px;
    font-weight: bold;
  }
  p { font-size: 12px;
    a { text-decoration: none;
      &:hover { border-width: 1px }
    }
  }
}

Pro
Modern features and mixins

Less contains the base feature-set for a CSS preprocessor:

Nesting
Variables
Basic mathematical operations
Color functions
@import
Basic type functions

Pro
Popular

Less is one of the most popular preprocessors due to being the easy to learn and its use in Twitter Bootstrap.

Pro
Less is written in JavaScript

Many web developers are familiar with JavaScript and because Less is written in JS, it can be processed client side making the set-up easy.

Pro
GUI apps

Apps such as Crunch, SimpLESS, WinLess, Koala, CodeKit, LiveReload or Prepros will watch and compile less.js for you.

Pro
Good IDE support

IDEs such as VS Code, Visual Studio and WebStorm (and other JetBrains IDEs) support LESS either natively or through plugins.

Pro
Readable syntax

By using whitespaces and nesting, you don't need braces or semicolons. This helps with keeping the syntax as readable and minimal as possible.

Pro
Supports variables out of the box

Sly has out of the box support for variables.

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Cons

Con
Less uses '@' to declare variables

The '@' symbol is used with Less to declare variables. However '@' already has meaning in CSS, as it is used to declare @media queries and @keyframes. This can result in some confusion when reading the code.

Con
calc() requires interpolation

Con
Limited support of conditionals

Less currently has limited support of conditionals such as ternary operators.

Con
No custom functions

Less does not offer custom functions and instead requires the use of mixins. This is limiting in many ways - Functions cannot be called on shorthand values, they cannot return a value, and code needs to be repeated depending on where the mixin is needed.

Con
Noisy syntax

Many unnecessary characters such as the following:

 {}:;@

Con
No loop and conditionals block

Con
Extremely limited adoption

Sly has just 5 stars on Github and a very small adoption rate. For an open source project this usually means less bugs reported, lesser documentation and few third-party learning resources.