Check if String is a Valid Number in JavaScript-Code Examples

function isValidNumber(str) {
  // if the string is empty, it's not a valid number
  if (str === "") {
    return false;
  }

  // if the string contains anything other than digits, it's not a valid number
  if (/\D/.test(str)) {
    return false;
  }

  // if the string starts with 0 and is longer than 1 character, it's not a valid number
  if (str.charAt(0) === "0" && str.length > 1) {
    return false;
  }

  // if we get to this point, the string is a valid number
  return true;
}

const isValidNumber = str => {
  // check if string is empty
  if (str === "") return false;

  // convert string to number
  const num = Number(str);

  // check if string is a number
  if (isNaN(num)) return false;

  // check if number is finite
  if (!isFinite(num)) return false;

  // return true if string is a valid number
  return true;
};