AI solution for JavaScript Coding Question on BFE.dev
166. validate number string

One possible solution to this problem is to use regular expressions to match the string against the different formats of valid numbers.

Here's an example implementation:

function validateNumberString(str) {
  // integer: optional sign, then at least one digit
  let integerRegex = /^[-+]?\d+$/;
  
  // decimal number: optional sign, then at least one digit, then optional decimal point followed by at least one digit
  let decimalRegex = /^[-+]?\d+(\.\d+)?$/;
  
  // exponential notation: optional sign, then at least one digit, then optional decimal point followed by at least one digit, then "e" or "E" followed by optional sign and at least one digit
  let exponentialRegex = /^[-+]?\d+(\.\d+)?([eE][-+]?\d+)?$/;
  
  return integerRegex.test(str) || decimalRegex.test(str) || exponentialRegex.test(str);
}

The function uses RegExp.test() method to check if the string matches any of the regular expressions defined for each format. The ^ and $ characters at the beginning and end of each regex ensure that the entire string is matched, so there can be no trailing or leading characters that are not part of the number.

Note that this implementation only matches numbers that are in base 10. If you need to support other bases, you may need to modify the regexes accordingly. Also, it treats empty string as invalid, so you may need to add additional logic to handle that case.