lodash/_createRound.js

define(['./toInteger', './toNumber', './toString'], function(toInteger, toNumber, toString) {

  /**
   * Creates a function like `_.round`.
   *
   * @private
   * @param {string} methodName The name of the `Math` method to use when rounding.
   * @returns {Function} Returns the new round function.
   */
  function createRound(methodName) {
    var func = Math[methodName];
    return function(number, precision) {
      number = toNumber(number);
      precision = toInteger(precision);
      if (precision) {
        // Shift with exponential notation to avoid floating-point issues.
        // See [MDN](https://mdn.io/round#Examples) for more details.
        var pair = (toString(number) + 'e').split('e'),
            value = func(pair[0] + 'e' + (+pair[1] + precision));

        pair = (toString(value) + 'e').split('e');
        return +(pair[0] + 'e' + (+pair[1] - precision));
      }
      return func(number);
    };
  }

  return createRound;
});