isValidNumber.js

isNumber.js

/*
Validate if a given string can be interpreted as a decimal number.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
" -90e3   " => true
" 1e" => false
"e3" => false
" 6e-1" => true
" 99e2.5 " => false
"53.5e93" => true
" --6 " => false
"-+3" => false
"95a54e53" => false

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

Numbers 0-9
Exponent - "e"
Positive/negative sign - "+"/"-"
Decimal point - "."
Of course, the context of these characters also matters in the input.
*/

/**
 * @param {string} s
 * @return {boolean}
 */
var isNumber = function(s = '') {    

    function trim(s = '') {
      let startIndex = -1, endIndex = -1;
      let leftTrimmed = '', trimmed = '';

      for(let i = 0; i < s.length; i++) {
        if(s[i] !== ' ') {
          startIndex = i;
          break;
        }
      }

      for(let j = s.length -1; j > -1; j--) {
        if(s[j] !== ' ') {
          endIndex = j;
          break;
        }
      }

      for(let k = startIndex; k <= endIndex; k++) {
        trimmed += s[k];
      }
      return trimmed;
    }
    
    try {
        const isNotNumber = function isNotNumber(value) {
            return value !== null && (value != value || +value != value);
        }

        return !isNotNumber(trim(s));
    } catch (e) {
        return false;
    }    
};