string-math.js

/*MIT License
Copyright (c) 2017 Paweł Rafałko dev.rafalko@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of 
this software and associated documentation files (the "Software"), to deal in 
the Software without restriction, including without limitation the rights to use, 
copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the 
Software, and to permit persons to whom the Software is furnished to do so, 
subject to the following conditions:

The above copyright notice and this permission notice **shall be included** in 
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/
function stringMath(eq, callback) {
  if (typeof eq !== 'string') return handleCallback(new TypeError('The [String] argument is expected.'), null);
  const mulDiv = /([+-]?\d*\.?\d+(?:e[+-]\d+)?)\s*([*/])\s*([+-]?\d*\.?\d+(?:e[+-]\d+)?)/;
  const plusMin = /([+-]?\d*\.?\d+(?:e[+-]\d+)?)\s*([+-])\s*([+-]?\d*\.?\d+(?:e[+-]\d+)?)/;
  const parentheses = /(\d)?\s*\(([^()]*)\)\s*/;
  var current;
  while (eq.search(/^\s*([+-]?\d*\.?\d+(?:e[+-]\d+)?)\s*$/) === -1) {
    eq = fParentheses(eq);
    if (eq === current) return handleCallback(new SyntaxError('The equation is invalid.'), null);
    current = eq;
  }
  return handleCallback(null, +eq);

  function fParentheses(eq) {
    while (eq.search(parentheses) !== -1) {
      eq = eq.replace(parentheses, function (a, b, c) {
        c = fMulDiv(c);
        c = fPlusMin(c);
        return typeof b === 'string' ? b + '*' + c : c;
      });
    }
    eq = fMulDiv(eq);
    eq = fPlusMin(eq);
    return eq;
  }

  function fMulDiv(eq) {
    while (eq.search(mulDiv) !== -1) {
      eq = eq.replace(mulDiv, function (a) {
        const sides = mulDiv.exec(a);
        const result = sides[2] === '*' ? sides[1] * sides[3] : sides[1] / sides[3];
        return result >= 0 ? '+' + result : result;
      });
    }
    return eq;
  }

  function fPlusMin(eq) {
    eq = eq.replace(/([+-])([+-])(\d|\.)/g, function (a, b, c, d) { return (b === c ? '+' : '-') + d; });
    while (eq.search(plusMin) !== -1) {
      eq = eq.replace(plusMin, function (a) {
        const sides = plusMin.exec(a);
        return sides[2] === '+' ? +sides[1] + +sides[3] : sides[1] - sides[3];
      });
    }
    return eq;
  }

  function handleCallback(errObject, result) {
    if (typeof callback !== 'function') {
      if (errObject !== null) throw errObject;
    } else {
      callback(errObject, result);
    }
    return result;

  }

}

if (typeof module !== 'undefined' && typeof exports !== 'undefined' && module.exports) {
  module.exports = stringMath;
}