get-ordinal-number.js

function getOrdinalNumber(num) {
  // This is for num argument validation that go inside the function.
  if ( !Number.isInteger(num)) {
    throw new Error("Invalid input: the value must be a number");
  }

  // This allow float number to be round into it nearest integer.
  const mainReminder = num % 100;
  const secondReminder = num % 10;

  if (mainReminder === 11 || mainReminder === 12 || mainReminder === 13) {
    return `${num}th`;
  }
  switch (true) {
    case secondReminder === 1:
      return `${num}st`;
    case secondReminder === 2:
      return `${num}nd`;
    case secondReminder === 3:
      return `${num}rd`;
    default:
      return `${num}th`;
  }
}

module.exports = getOrdinalNumber;

function testAssert(inputNumber, outputNUmber) {
  console.assert(
    inputNumber === outputNUmber,
    `Test failed: expected ${outputNUmber}, but got ${inputNumber}`
  );
}
//Basic test of first digit integer
testAssert(getOrdinalNumber(1), "1st");
testAssert(getOrdinalNumber(2), "2nd");
testAssert(getOrdinalNumber(3), "3rd");
testAssert(getOrdinalNumber(4), "4th");
//Test for 11, 12 and 13
testAssert(getOrdinalNumber(11), "11th");
testAssert(getOrdinalNumber(12), "12th");
testAssert(getOrdinalNumber(13), "13th");
//Test for double digit number
testAssert(getOrdinalNumber(21), "21st");
testAssert(getOrdinalNumber(32), "32nd");
testAssert(getOrdinalNumber(43), "43rd");
//Normal number and float number test.
testAssert(getOrdinalNumber(101), "101st");
testAssert(getOrdinalNumber(202), "202nd");
testAssert(() => getOrdinalNumber(1.2), "Invalid input");
testAssert(() => getOrdinalNumber(10.51), "Invalid input");