Creates a high resolution timer. Call with a name to start. Call with a new name to "lap". Call with no arguments to stop.

createTimer.js

function createTimer (log) {
    let prev = null;
    function hrtimeDurationToMs([durS, durUs]) {
        return ((durS * 1000) + (durUs / 1000000)).toFixed(4);
    }
    return (name = null) => {
        if (prev) {
            const dur = hrtimeDurationToMs(process.hrtime(prev[1]));
            log(`end ${prev[0]}, took ${dur}ms`, { name: prev[0], hrtime: prev[1], dur });
        }
        if (name) {
            const hrtime = process.hrtime();
            prev = [name, hrtime];
            log(`start ${name}`, { name, hrtime });
        } else {
            prev = null;
        }
    };
}