Equation.js/lib/operators.js

import Equation from 'equation';

/*
 * Operators and Functions
 * fn: function used to evaluate value
 * format: the format using which arguments are parsed:
 *         0 indicates an argument and 1 indicates the operator
 *         e.g: factorial is 01, add is 010, like 2!, 2+2
 * precedence: determines which operators should be evaluated first
 *             the lower the value, the higher the precedence
 * hasExpression: determines if any of the operator arguments are an expression
 *                This way, arguments will not be solved by equation and instead
 *                you have to call solve on each argument yourself.
 *                You get the arguments as parsed arrays sigma(0, 5, 2@) becomes
 *                sigma(0, 5, [2, '*', '@']). See sigma operator for reference
 */
export default {
  '^': {
    fn: (a, b) => Math.pow(a, b),
    format: '010',
    precedence: 0
  },
  '*': {
    fn: (a, b) => a * b,
    format: '010',
    precedence: 1
  },
  '/': {
    fn: (a, b) => a / b,
    format: '010',
    precedence: 1
  },
  '%': {
    fn: (a, b) => a % b,
    format: '010',
    precedence: 1
  },
  '\\': {
    fn: (a, b) => Math.floor(a / b),
    format: '010',
    precedence: 1
  },
  '+': {
    fn: (a, b) => a + b,
    format: '010',
    precedence: 2
  },
  '-': {
    fn: (a, b) => a - b,
    format: '010',
    precedence: 2
  },
  '!': {
    fn: (a) => {
      let sum = 1;
      for (var i = 0; i < a; ++i) {
        sum *= i;
      }
      return sum;
    },
    format: '01',
    precedence: 2
  },
  'log': {
    fn: Math.log,
    format: '10',
    precedence: -1
  },
  'ln': {
    fn: Math.log,
    format: '10',
    precedence: -1
  },
  'lg': {
    fn: (a) => Math.log(a) / Math.log(2),
    format: '10',
    precedence: -1
  },
  'sin': {
    fn: Math.sin,
    format: '10',
    precedence: -1
  },
  'cos': {
    fn: Math.cos,
    format: '10',
    precedence: -1
  },
  'tan': {
    fn: Math.tan,
    format: '10',
    precedence: -1
  },
  'cot': {
    fn: Math.cot,
    format: '10',
    precedence: -1
  },
  'round': {
    fn: Math.round,
    format: '10',
    precedence: -1
  },
  'floor': {
    fn: Math.floor,
    format: '10',
    precedence: -1
  },
  'sigma': {
    fn(from, to, expression) {
      const expr = expression.join('').replace(/,/g, '');
      const regex = new RegExp(ITERATOR_SIGN, 'g');

      let sum = 0;
      for (let i = from; i <= to; i++) {
        sum += Equation.solve(expr.replace(regex, i));
      }
      return sum;
    },
    format: '1000',
    hasExpression: true,
    precedence: -1
  }
};

const ITERATOR_SIGN = '@';