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V2 Upgrade Guide

Language Changes

Colours now output as they are written, so purple stays as purple and is not converted to its hex representation.

Command Line Usage

Clean CSS

We have removed the dependency on clean-css and moved it to a plugin. This allows us to:

  1. update the dependency and integration without a Less release
  2. not tie people who do not use clean-css into having it downloaded by npm.

The usage is similar, just install the plugin (npm install -g less-plugin-clean-css) then tell less to use it by using the --clean-css argument.

# old
lessc --clean-css --clean-option=--compatibility:ie8 --clean-option=--advanced
# new
lessc --clean-css="--compatibility=ie8 --advanced"


We have improved the source map options and path generation so the sourcemap should be generated at the correct path without specifying any options.

Programmatic Usage

We have deprecated the use of less.Parser and toCss to generate the css. Instead we require you to use the less.render shorthand. See Programmatic Usage for more information.

Further, instead of returning a string which is the css, we return an object with a css field set to the string and a map field set to the sourcemap (if applicable).

The sourcemap options are now to be set on sourceMap instead of directly on options. So instead of options.sourceMapFullFilename = you would set options.sourceMap = { sourceMapFullFilename: .

Browser Usage

The browser usage has not changed significantly. Options set on the less object are exposed as less.options after the less script has run, rather than polluting less.

It is now possible to specify options on the script and Less tags, which should simplify option setting in the browser. See the browser usage section for more information.

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