calculator-engine.js

"use strict";
/**
 * Name: Calculator
 * Author: Tom Wilson
 * Description: This is a calculator engine that provides the ability to 
 * set the operators functions that will be used in the calculation process
 * this gives the student the ability to create the operator functions of the 
 * calculator process, without having to worry about the engine.
 * The main calc method takes a string as an equation:
 * 
 * Calculator.calc('1 + 1')
 * 
 * If you have your operators set, the engine should work fine.
*/

(function (window) {

  window.Calculator = {
    setOperator: setOperator,
    calc: calculate
  };

  var methods = {};

  function calculate(expr) {
    return expr.split(' ').reduce(calc, 0);
  }

  function calc(acc, x) {
    if (x === '+' && isNumber(acc)) {
      return methods.ADD(parseInt(acc, 10));
    }
    if (x === '-' && isNumber(acc)) {
      return methods.MINUS(parseInt(acc, 10));
    }
    if (x === '*' && isNumber(acc)) {
      return methods.TIMES(parseInt(acc, 10));
    }
    if (x === '/' && isNumber(acc)) {
      return methods.DIVIDE(parseInt(acc, 10));
    }

    if (isFunction(acc)) {
      return acc(parseInt(x, 10));
    }

    return x;
  }
  function setOperator(operator, fn) {
    // check if valid operator
    if (/(\+|\-|\*|\/)/.test(operator) === false) {
      throw new Error('Operator must be either + or - or * or /');
    }
    if (operator === '+') {
      methods.ADD = curry(fn);
    } else if (operator === '-') {
      methods.MINUS = curry(fn);
    } else if (operator === '*') {
      methods.TIMES = curry(fn);
    } else if (operator === '/') {
      methods.DIVIDE = curry(fn);
    }
  }

  function isNumber(v) {
    v = parseInt(v, 10);
    return typeof v === 'number' ? true : false;
  }

  function isFunction(v) {
    return typeof v === 'function' ? true : false;
  }

  function curry(fn) {
    return function (a) {
      return function (b) {
        return fn(a, b);
      };
    };
  }
})(window);

// usage example
/*
  Calculator.setOperator('+', function (a,b) {
    return a + b
  })
  
  Calculator.setOperator('-', function (a,b) {
    return a - b
  })
  Calculator.enter('12 + 12') // 24
*/