function isNumeric(s) {
      if (s == undefined) {
        return false;
      }
      let hasPoint = false;
      let hasExp = false;
      for (let i = 0; i < s.length; i++) {
        const target = s[i];
        if (target >= 0 && target <= 9) {
          continue;
        } else if (target === 'e' || target === 'E') {
          if (hasExp || i === 0 || i === s.length - 1) {
            return false;
          } else {
            hasExp = true;
            continue;
          }
        } else if (target === '.') {
          if (hasPoint || hasExp || i === 0 || i === s.length - 1) {
            return false;
          } else {
            hasPoint = true;
            continue;
          }
        } else if (target === '-' || target === '+') {
          if (i === 0 || s[i - 1] === 'e' || s[i - 1] === 'E') {
            continue;
          } else {
            return false;
          }
        } else {
          return false;
        }
      }
      return true;
    }