js
var libCoverage = require('istanbul-lib-coverage');
var map = libCoverage.createCoverageMap(globalCoverageVar);
var summary = libCoverage.createCoverageSummary();

// merge another coverage map into the one we created
map.merge(otherCoverageMap);

// inspect and summarize all file coverage objects in the map
map.files().forEach(function(f) {
    var fc = map.fileCoverageFor(f),
        s = fc.toSummary();
    summary.merge(s);
});

console.log('Global summary', summary);