How to generate source maps with Node.js and uglify2 js?

Question

I am using this code

function makeJS(pathArray, outfile) {
    var result = uglifyJS.minify(pathArray, {
        'compress': {
            global_defs: {
                DEBUG: false
            }
        }
    });
    writeFile(outfile, result.code);
}

https://github.com/mishoo/UglifyJS2

to generate a combined minified js file, but now I want to generate a source map so I can still debug with the minified file, however I can't find any documentation on how to create the source map in Node.js code. Does anyone know how to do it?

Thanks