randomDateOfBirth JavaScript function for generating sample DOB within an age range

randomDateOfBirth.js

function assert(condition, message) {
  if (!condition) {
    throw new Error("Assertion failed: [" + (message || "no message") + "]" );
  }
}

function randomDate(start, end) {
  assert(start < end,"start < end");
  return new Date(start.getTime() + Math.random() * (end.getTime() - start.getTime()));
}

function randomDateOfBirth(minAge = 0, maxAge = 121, asOfDate = new Date()) {
  assert(minAge>=0,"minAge>=0");
  assert(maxAge<=999,"maxAge<=999");
  assert(minAge<=maxAge,"minAge<=maxAge");
  
  var d = randomDate(new Date( asOfDate.getFullYear()-maxAge , 0, 1), new Date(asOfDate.getFullYear()-minAge, 11, 31));
  d.setHours(0,0,0,0); //optionally adjust datetime to midnight local time
  return d;
}

//Usage:
const random_dob = randomDateOfBirth(18,65);

console.log("Date with time and tz:",random_dob.toISOString()); //"Date with time and tz:", "1947-05-19T00:00:00.000Z"
console.log("Date only:",random_dob.toISOString().slice(0,10)); //"Date only:", "1947-05-19"