Code Review (Easy): Refining Metric Inputs

Story

Mark Patel was updating the shared utility library at ReviewThat Labs to better handle the various ways developers input performance metrics into the dashboard. Eva Harrington pointed out that the previous version was too strict, failing on valid shorthand like trailing decimals or scientific notation used for high-frequency data. Mark is now refining the logic to ensure that inputs like "-123.456e789" pass through smoothly, while clearly broken entries like "95a54e53" are caught and rejected. This update will help the team reuse the same validation logic across all their internal monitoring tools.

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Read the story and code, then decide if the code is ready for production or needs improvement.

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export function isNumber(s: string): boolean {
  function isWhitespace(ch: string): boolean {
    // common whitespace characters
    return ch === ' ' || ch === '\n' || ch === '\r' || ch === '\t' || ch === '\f' || ch === '\v' || ch === '\u00A0' || ch === '\u2028' || ch === '\u2029';
  }

function isDigit(ch: string): boolean {
    return ch >= '0' && ch <= '9';
  }

const str = trimCustom(s);
  if (str.length === 0) return false;

let i = 0;
  const n = str.length;

// optional sign
  if (i < n && (str.charAt(i) === '+' || str.charAt(i) === '-')) {
    i++;
  }

let digitsBefore = 0;
  while (i < n && isDigit(str.charAt(i))) {
    digitsBefore++;
    i++;
  }

let digitsAfter = 0;
  if (i < n && str.charAt(i) === '.') {
    i++;
    while (i < n && isDigit(str.charAt(i))) {
      digitsAfter++;
      i++;
    }
  }

if (digitsBefore === 0 && digitsAfter === 0) {
    return false;
  }

if (i < n && (str.charAt(i) === 'e' || str.charAt(i) === 'E')) {
    i++;
    if (i < n && (str.charAt(i) === '+' || str.charAt(i) === '-')) {
      i++;
    }
    let digitsExp = 0;
    while (i < n && isDigit(str.charAt(i))) {
      digitsExp++;
      i++;
    }
    if (digitsExp === 0) return false;
  }

return i === n;
}