The use case for this came from trying to get coverage reports for an Angular/AngularJS hybrid application. Angular uses the angular-cli which uses the karma-coverage-istanbul-reporter under the hood. Some guides would say to use karma-coverage and the report type of in-memory to create a report in memory so that it can instrument your AngularJS code. While this works fine for summary reports, you were not able to drill down into html reports to see AngularJS code because karma-coverage does not use the istanbul-lib-coverage from the istanbul-api but rather the Instrumenter direct from istanbul. This is just a simple wrapper which calls that under the hood.

karma.conf.js (modified from an angular-cli generated app)

{
    plugins: [
        require('karma-coverage-istanbul-es5-preprocessor')
    ],
    preprocessors: {
        './src/**/*.js': ['coverage-istanbul-es5']
    },
    coverageIstanbulReporter: {
        dir: paths.results + '/coverage',
        reports: [
            'html',
            'text-summary'
        ],
        fixWebpackSourcePaths: true
    },
    reporters: [
        'progress',
        'coverage-istanbul'
    ],
}