Compiling LESS from a node.js script

Compiling LESS from a node.js script

onedayitwillmake 2 comments
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LESS is a tool that allows you to write CSS in a programmer friendly way (with variables, and some simple functions), it then converts it to regular CSS for browser friendly consumption.

It’s amazingly easy to use, during development you don’t have to change a thing.
You simply import your .less file, then under you import ‘less.js’ and it does it’s magic.

Eventually you need to preprocess it as part of your build operation.

For some reason I could not find a simple response for how to do this.
I found many articles / answers for how to run LESS from the command line, or using it with Express to pre-compile it for you when serving then cache it.

Here’s what I ended up using, much of it referenced from the lessc command line tool.

var less = require( 'less' );
var fs = require( 'fs' );
var path = require('path');
 
 
// Load the file, convert to string
fs.readFile( '../less/gaf.less', function ( error, data ) {
  var dataString = data.toString();
  var options = {
    paths         : ["../less"],      // .less file search paths
    outputDir     : "../css",   // output directory, note the '/'
    optimization  : 1,                // optimization level, higher is better but more volatile - 1 is a good value
    filename      : "gaf.less",       // root .less file
    compress      : true,             // compress?
    yuicompress   : true              // use YUI compressor?
  };
 
 
  // Create a file name such that
  //  if options.filename == gaf.js and options.compress = true
  //    outputfile = gaf.min.css
  options.outputfile = options.filename.split(".less")[0] + (options.compress ? ".min" : "") + ".css";
  // Resolves the relative output.dir to an absolute one and ensure the directory exist
  options.outputDir = path.resolve( process.cwd(), options.outputDir) + "/";
  ensureDirectory( options.outputDir );
 
  // Create a parser with options, filename is passed even though its loaded
  // to allow less to give us better errors
  var parser = new less.Parser(options);
  parser.parse( dataString, function ( error, cssTree ) {
      if ( error ) {
        less.writeError( error, options );
        return;
      }
 
    // Create the CSS from the cssTree
    var cssString = cssTree.toCSS( {
      compress   : options.compress,
      yuicompress: options.yuicompress
    } );
 
    // Write output
    fs.writeFileSync( options.outputDir + options.outputfile, cssString, 'utf8' );
    console.log("Converted Less: '" + options.filename + "', to CSS: " + options.outputDir + options.outputfile);
  });
});
 
//
var ensureDirectory = function (filepath) {
  var dir = path.dirname(filepath);
  var existsSync = fs.existsSync || path.existsSync;
  if (!existsSync(dir)) { fs.mkdirSync(dir); }
};

2 Comments

Yoboy

September 3, 2014 at 10:57 pm

Thx a lot, i found didn’t found the doc for the nodejs part of less :/

You were a great help.

 Reply

Camilo Martin

September 6, 2014 at 12:08 am

Thanks! I went to read lessc source’s anyway but your post helped me out.

 Reply

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