internal/equalByTag.js

define(['./baseToString'], function(baseToString) {

  /** `Object#toString` result references. */
  var boolTag = '[object Boolean]',
      dateTag = '[object Date]',
      errorTag = '[object Error]',
      numberTag = '[object Number]',
      regexpTag = '[object RegExp]',
      stringTag = '[object String]';

  /**
   * A specialized version of `baseIsEqualDeep` for comparing objects of
   * the same `toStringTag`.
   *
   * **Note:** This function only supports comparing values with tags of
   * `Boolean`, `Date`, `Error`, `Number`, `RegExp`, or `String`.
   *
   * @private
   * @param {Object} value The object to compare.
   * @param {Object} other The other object to compare.
   * @param {string} tag The `toStringTag` of the objects to compare.
   * @returns {boolean} Returns `true` if the objects are equivalent, else `false`.
   */
  function equalByTag(object, other, tag) {
    switch (tag) {
      case boolTag:
      case dateTag:
        // Coerce dates and booleans to numbers, dates to milliseconds and booleans
        // to `1` or `0` treating invalid dates coerced to `NaN` as not equal.
        return +object == +other;

      case errorTag:
        return object.name == other.name && object.message == other.message;

      case numberTag:
        // Treat `NaN` vs. `NaN` as equal.
        return (object != +object)
          ? other != +other
          // But, treat `-0` vs. `+0` as not equal.
          : (object == 0 ? ((1 / object) == (1 / other)) : object == +other);

      case regexpTag:
      case stringTag:
        // Coerce regexes to strings and treat strings primitives and string
        // objects as equal. See https://es5.github.io/#x15.10.6.4 for more details.
        return object == baseToString(other);
    }
    return false;
  }

  return equalByTag;
});