Simple grunt task for instrumenting javascript files and then generating reports from coverage data

grunt-coverage.js

grunt.registerMultiTask('coverage', function () {

    if (this.target === 'instrument') {

        var ignore = this.data.ignore || [];
        var Instrumenter = require('istanbul').Instrumenter;
        var instrumenter = new Instrumenter();

        this.files.forEach(function (file) {

            var src = file.src[0];
            var instrumented = grunt.file.read(src);

            // only instrument this file if it is not in ignored list
            if (!grunt.file.isMatch(ignore, src)) {
                instrumented = instrumenter.instrumentSync(instrumented, src);
            }

            // write
            grunt.file.write(file.dest, instrumented);
        });

        return;
    }

    if (this.target === 'report') {

        this.requiresConfig('coverage.coverage');

        var istanbul = require('istanbul');
        var Report = istanbul.Report;
        var Collector = istanbul.Collector;

        var reporters = this.data.reports;
        var dest = this.data.dest;

        var collector = new Collector();

        collector.add(grunt.config('coverage.coverage'));

        reporters.forEach(function (reporter) {
            Report.create(reporter, {
                dir: dest + reporter
            }).writeReport(collector, true);
        });

        return;
    }

    grunt.warn('Unknown target - valid targets are "instrument" and "report"');

});

Gruntfile.js

module.exports = function (grunt) {
    
    grunt.initConfig({
        
        coverage: {
            
            // set this to the coverage object created from running the instrumented code
            coverage: null,
            
            // task for generating instrumented code
            instrument: {
                
                // files to NOT instrument eg. libs
                ignore: [
                    'src/js/libs/**/*'
                ],
                
                // file to instrument
                files: [
                    {
                        src: '**/*.js',
                        expand: true,
                        cwd: 'src',
                        dest: 'instrumented'
                    }
                ]
            },
            
            // task for generating reports
            report: {
                reports: ['html', 'text-summary'],
                dest: 'tests/reports/'
            }
        }
        
    });
    
};