validateNumber

Checks if the given value is a number.

• Use parseFloat() to try to convert n to a number.
• Use !Number.isNaN() to check if num is a number.
• Use Number.isFinite() to check if num is finite.
• Use Number() and the loose equality operator (==) to check if the coercion holds.

const validateNumber = n => {
  const num = parseFloat(n);
  return !Number.isNaN(num) && Number.isFinite(num) && Number(n) == n;
}

validateNumber('10'); // true
validateNumber('a'); // false