mathjs/lib/type/BigNumber.js

var Decimal = require('decimal.js');
var digits = require('../util/number').digits;

function factory (type, config, load, typed) {
  var BigNumber = Decimal.constructor(config);

  /**
   * Get a JSON representation of a BigNumber containing
   * type information
   * @returns {Object} Returns a JSON object structured as:
   *                   `{"mathjs": "BigNumber", "value": "0.2"}`
   */
  BigNumber.prototype.toJSON = function () {
    return {
      mathjs: 'BigNumber',
      value: this.toString()
    };
  };

  /**
   * Instantiate a BigNumber from a JSON object
   * @param {Object} json  a JSON object structured as:
   *                       `{"mathjs": "BigNumber", "value": "0.2"}`
   * @return {BigNumber}
   */
  BigNumber.fromJSON = function (json) {
    return new BigNumber(json.value);
  };

  // TODO: remove BigNumber.convert as soon as it's deprecated
  // extend BigNumber with a function convert
  if (typeof BigNumber.convert !== 'function') {
    /**
     * Try to convert a Number in to a BigNumber.
     * If the number has 15 or mor significant digits, the Number cannot be
     * converted to BigNumber and will return the original number.
     * @param {Number} number
     * @return {BigNumber | Number} bignumber
     */
    BigNumber.convert = function(number) {
      if (digits(number) > 15) {
        return number;
      }
      else {
        return new BigNumber(number);
      }
    };
  }
  else {
    throw new Error('Cannot add function convert to BigNumber: function already exists');
  }

  return BigNumber;
}

exports.name = 'BigNumber';
exports.path = 'type';
exports.factory = factory;