timeit.js

function timeit(fn, count, pars)
{
    performance.measure('start');
    for(let i = 0; i < count; i++)
    {
        fn(...pars);
    }
    performance.measure('end');
    starts = performance.getEntriesByName('start')
    ends = performance.getEntriesByName('end')
    performance.clearMeasures('start');
    performance.clearMeasures('end');
    return ends[ends.length-1].duration - starts[starts.length-1].duration
}