The memory usage logger for a Node.js process

index.js

/**
 * The memory usage logger for a Node.js process
 * 
 * Resident Set Size (RSS) is the amount of space occupied in the main memory
 * device for the process, which includes the heap, code segment and stack.
 * Variables are stored in the stack and the actual JavaScript code resides in the code segment.
 *
 * The heap is where objects, strings, and closures are stored.
 *
 * @see https://nodejs.org/api/process.html#process_process_memoryusage
 */
setInterval(function () {
  const mem = process.memoryUsage();

  function fmt(v) {
    return (v / (1024 * 1024)).toFixed(3);
  }

  console.error(
    'RSS = ' + fmt(mem.rss) + ', ' +
    'Heap Total = ' + fmt(mem.heapTotal) + ', ' +
    'Heap Used = ' + fmt(mem.heapUsed)
  );
}, 5000);