How to use the nyc/node_modules/istanbul-lib-report.createContext function in nyc

var map = libCoverage.createCoverageMap(JSON.parse(fs.readFileSync(fullPath, 'utf8')));
        if (mergedCoverageMap !== null) {
            mergedCoverageMap.merge(map);
        }
        else {
            mergedCoverageMap = map;
        }
    }
}

if (mergedCoverageMap === null) {
    console.warn('Warning: No cover files to be merged');
    return;
}

var context = libReport.createContext({
    dir: path.join(rootFolder, mergeIntoFolder)
});

tree = libReport.summarizers.pkg(mergedCoverageMap);

tree.visit(reports.create('html'), context);
tree.visit(reports.create('lcov'), context);

fs.writeFileSync(path.join(rootFolder, '..', '..', '.nyc_output', 'coverage-final.json'), JSON.stringify(mergedCoverageMap.toJSON()));