Less.js

LESS stands for Leaner CSS, and is an extension for the CSS language, adding support for variables, nested rules, mixins and operations.

LESS currently supports both CSS 2 & 3 syntax and is a widely used language amongst developers.

Less.js is a JavaScript library capable of reading LESS syntax.

The library is basically a CSS preprocessor, taking .less files and converting their content to standards compliant CSS code, also saving it to a new file in classic .css format which every browser can interpret.

Both LESS (the syntax) and Less.js (the library) have seen usage in large companies around the Internet, starting with Google, Twitter and Facebook.

What is new in this release:

• Supports the scoped @plugin directive to load function plugins
• All directives are bubbled (e.g. supports), not just media
• Performance improvements to the parser - should help non-chrome browsers with very large less files to be a lot quicker.
• The image size function respects include paths like other file functions
• Color functions take a relative argument that applies percentages relatively instead of absolutely
• Include paths now allows : as a separator on windows (recognizing and not splitting drive names by the backslash)
• @import (CSS) does not pull the directive above comments
• Fix for import statements without quotes sometimes causing issues
• Replace supports dimensions and colors
• The browser field is set in the package.json for use with Browserify
• Another fix to support paths being passed as a string instead of an array
• Detached rulesets can be used as default arguments
• Fixed alot of false warnings about extends
• Errors written to stderr more consistently
• Consistently keep units if strict units is off
• Better support for comments in function all arguments

What is new in version 2.5.1:

• Supports the scoped @plugin directive to load function plugins
• All directives are bubbled (e.g. supports), not just media
• Performance improvements to the parser - should help non-chrome browsers with very large less files to be a lot quicker.
• The image size function respects include paths like other file functions
• Color functions take a relative argument that applies percentages relatively instead of absolutely
• Include paths now allows : as a separator on windows (recognizing and not splitting drive names by the backslash)
• @import (CSS) does not pull the directive above comments
• Fix for import statements without quotes sometimes causing issues
• Replace supports dimensions and colors
• The browser field is set in the package.json for use with Browserify
• Another fix to support paths being passed as a string instead of an array
• Detached rulesets can be used as default arguments
• Fixed alot of false warnings about extends
• Errors written to stderr more consistently
• Consistently keep units if strict units is off
• Better support for comments in function all arguments

What is new in version 2.5.0:

• Supports the scoped @plugin directive to load function plugins
• All directives are bubbled (e.g. supports), not just media
• Performance improvements to the parser - should help non-chrome browsers with very large less files to be a lot quicker.
• The image size function respects include paths like other file functions
• Color functions take a relative argument that applies percentages relatively instead of absolutely
• Include paths now allows : as a separator on windows (recognizing and not splitting drive names by the backslash)
• @import (CSS) does not pull the directive above comments
• Fix for import statements without quotes sometimes causing issues
• Replace supports dimensions and colors
• The browser field is set in the package.json for use with Browserify
• Another fix to support paths being passed as a string instead of an array
• Detached rulesets can be used as default arguments
• Fixed alot of false warnings about extends
• Errors written to stderr more consistently
• Consistently keep units if strict units is off
• Better support for comments in function all arguments

What is new in version 2.4.0:

• Support for plugins that pre-process (to add libraries silently etc.)
• Empty sourcemaps now work
• Extract and Length functions now ignore comments in a list (more work to come to fix the general problem)
• fragment url's are treated absolute since they refer to the html document
• Extends on a selector joined with & now work better
• Nested mixins work better with !important (regression in 2.3.0)
• The promise dependency is now actually optional (introduced in 2.0.0)
• Files with just \r newlines now process ok (regression in 2.0.0)
• When strict units is off and the unit is 1/x, (e.g. 1 / 12px) the unit output is x, previously nothing (regression in 2.0.0)

What is new in version 2.3.1:

• Fixed depends option (regression in 2.3.0)
• Support parent selector (&) used in sub element expression (e.g. :not(.c_&))

What is new in version 2.3.0:

• Added isruleset function.
• Added optional import option, causing less to not fail if file not found.
• Fixed browsers-side cache.
• Many fixes to import reference - support @support and keyframe.
• Selectors now interpolate pseudo selectors (e.g. :@{hover}).
• Fixed comments missed off if they were at the end of the file.
• Fixed !important used with parametric mixins.
• Emits warnings for extends when the target is not found.
• include-path now works on data-uri.
• Variables and function calls work for path in data-uri.
• Fixed absolute paths not working on imports sometimes.
• Unicode BOM removed again.

What is new in version 2.2.0:

• Using import filename interpolation and import inline together now works
• Deprecate the compression option (still works, but outputs a warning unless silent)
• The node version of less now has image-size, image-width, image-height which return the image dimensions of a file
• Fixed an issue that could cause the parse to occur more than once and the callback be called multiple times
• If you are outputting to the console, lessc defaults to silent so warnings do not end up in output
• isunit function supports '' to test if a dimension has no unit
• data-uri function now counts characters after base64 encoding instead of bytes before encoding to determine ie8 support
• Fixed bug effecting guards on pseudo class selectors
• Do not cache on the browser when used with modifyVars
• Detection if less does not parse last character in file
• Detection of whether a file is css now requires /css, .css, ?css, &css instead of just css. You can still tell less the type of file using import options.
• Removed extra new line added to sourcemap entry inline file
• Supports Safari extensions

What is new in version 2.1.0:

• Fixed isSync option, it was using sync file operations but promises are guaranteed to call back async. We now support promises as a feature rather than the 1st class way of doing things.
• Browser code is now synchronous again, like in v1, meaning it blocks the site until less is compiled
• Some fixes for variable imports which affected filemanagers when synchronous
• Fixed lessc makefile dependencies option
• Output now reports back a imports field with an array of imported files
• Relative path test for drive names (so windows only) is now case insensitive
• Fix for IE7 - use getChar instead of indexing array
• Variables using !important now output !important, which bubbles up to affect the rule
• LiveReload cache buster is now treated specially

What is new in version 2.0.0:

• Fixed multiplication in non strict units mode to take the left operand unit, in the case that the unit cannot be resolved
• Some fixes for browser cross-compatibility
• Browser tests now pass in IE 8-11 and FF
• Added index.js and browser.js in root as shortcuts
• Fixed some local variable spellings
• Support for @counter-style directive

What is new in version 1.7.4:

• Handle uppercase paths in browser
• Show error if an empty selector is used in extend
• Fixed property merging in directives
• Fixed ordering of charset and import directives
• Fixed race condition that caused a rules is undefined error sometimes if you had a complex import strategy
• Better error message for imports missing semi-colons or malformed

What is new in version 1.7.3:

• Do not round the results of color functions, like lightness, hue, luma etc..
• Support cover and contain keywords in background definitions.

What is new in version 1.7.0:

• Add support for rulesets in variables and passed to mixins to allow wrapping
• Change luma to follow the w3c spec, luma is available as luminance. Contrast still uses luma so you may see differences if your threshold % is close to the existing calculated luma.
• Upgraded clean css which means the --selectors-merge-mode is now renamed --compatibility
• Add support for using variables with @keyframes, @namespace, @charset
• Support property merging with +_ when spaces are needed and keep + for comma separated
• Imports now always import once consistently - a race condition meant previously certain configurations would lead to a different ordering of files

What is new in version 1.6.3:

• Fixed issue with calling toCSS twice not working in some situations.

What is new in version 1.6.1:

• Support ^ and ^^ shadow DOM selectors
• Fixed sourcemap selector (used to report end of the element or selector) and directive position (previously not supported)
• Fixed parsing empty less files
• Error on (currently) ambiguous guards on multiple CSS selectors
• Older environments - protect against typeof regex returning function
• Do not use default keyword

What is new in version 1.5.0:

• Support for import inline option to include css that you do NOT want less to parse e.g. @import (inline) "file.css";
• Better support for modifyVars (refresh styles with new variables, using a file cache), is now more resiliant
• Support for import reference option to reference external css, but not output it. Any mixin calls or extend's will be output.
• Support for guards on selectors (currently only if you have a single selector)
• Allow property merging through the +: syntax
• Added min/max functions
• Added length function and improved extract to work with comma seperated values
• When using import multiple, sub imports are imported multiple times into final output

What is new in version 1.4.1:

• Fixed syncImports and yui-compress option, as they were being ignored.
• Fixed several global variable leaks.

What is new in version 1.4.0:

• Fixed passing of strict maths option.

What is new in version 1.3.3:

• Fixed critical bug with mixin call if using multiple brackets.
• When using the filter contrast function, the function is passed through if the first argument is not a color.

What is new in version 1.3.2:

• Browser and server url re-writing is now aligned to not re-write (previous lessc behavior)
• URL-rewriting can be made to re-write to be relative to the entry file using the relative-urls option (less.relativeUrls option)
• rootpath option can be used to add a base path to every url
• Support mixin argument seperator of ';' so you can pass comma seperated values. e.g. .mixin(23px, 12px;);
• Fixed lots of problems with named arguments in corner cases, not behaving as expected
• hsv, hsva, unit functions
• Fixed lots more bad error messages
• Fixed @import-once to use the full path, not the relative one for determining if an import has been imported already
• Supports :not(:nth-child(3))

What is new in version 1.3.0:

• @media bubbling
• Support arbitrary entities as selectors
• Variadic argument support
• Behaviour of zero-arity mixins has changed, see link above.
• Allow '@import' directives in any selector
• Media-query features can now be a variable
• Automatic merging of media-query conditions
• Fix global variable leaks
• Fix error message on wrong-arity call
• Fix an '@arguments' behaviour bug
• Fix '::' selector output
• Fix a bug when using @media with mixins

Requirements:

• JavaScript enabled on client side
• Node.js 0.10 or higher for server-side environments