JavaScript: typr - deep type checking with error reports

typr.js

/**
 * typr - deep type checking with error reports
 * MIT licence
 */


;(function (root) {
  'use strict';

  /* ---------------------------------------------------------------------------
   * setup
   */

  var objectToString = Object.prototype.toString;

  function forOwn (object, fn) {
    Object.keys(object).forEach(function (key) {
      return fn(object[key], key, object);
    });
  }

  /* ---------------------------------------------------------------------------
   * main
   */

  function type (any) {
    var type = typeof any;
    return (
      any === null ? 'null' :
      // avoid webkit bug where `typeof /re/` yields 'function'
      type !== 'object' && type !== 'function' ? type :
      objectToString.call(any).slice(8, -1).toLowerCase()
    );
  }

  function matchesByType (any, expectedType) {

    return (function matchesByType_ (any, expectedType, errors, keychain){

      var metaType = type(expectedType),
          result;

      switch (metaType) {
        
        case 'string':
          result = type(any) === expectedType;
          break;
        
        case 'array':
          result = expectedType.reduce(function (result, expectedType, index) {
            return (result && matchesByType_(any[index], expectedType, errors, keychain.concat(i));
          }, type(any) === metaType);
          break;
        
        // case 'date':
        // case 'object':
        // case 'regexp':
        // case 'function':
        default:
          var result = type(any) === metaType;
          if (result) {
            forOwn(expectedType, function (expectedType, key) {
              return (result = result && matchesByType_(any[key], expectedType, errors, keychain.concat(key));
            });
          }
      }

      if (!result) errors.push(keychain);

      return errors;

    }(any, expectedType, [], []));
  }

  /* ---------------------------------------------------------------------------
   * export
   */

  root.typr = {
    type: type,
    matchesByType: matchesByType
  };

}(this));