meteor/packages/babel-runtime/babel-runtime.js

var hasOwn = Object.prototype.hasOwnProperty;

function canDefineNonEnumerableProperties() {
  var testObj = {};
  var testPropName = "t";

  try {
    Object.defineProperty(testObj, testPropName, {
      enumerable: false,
      value: testObj
    });

    for (var k in testObj) {
      if (k === testPropName) {
        return false;
      }
    }
  } catch (e) {
    return false;
  }

  return testObj[testPropName] === testObj;
}

// The name `babelHelpers` is hard-coded in Babel.  Otherwise we would make it
// something capitalized and more descriptive, like `BabelRuntime`.
babelHelpers = {
  // Meteor-specific runtime helper for wrapping the object of for-in
  // loops, so that inherited Array methods defined by es5-shim can be
  // ignored in browsers where they cannot be defined as non-enumerable.
  sanitizeForInObject: canDefineNonEnumerableProperties()
    ? function (value) { return value; }
    : function (obj) {
      if (Array.isArray(obj)) {
        var newObj = {};
        var keys = Object.keys(obj);
        var keyCount = keys.length;
        for (var i = 0; i < keyCount; ++i) {
          var key = keys[i];
          newObj[key] = obj[key];
        }
        return newObj;
      }

      return obj;
    },

  // es6.templateLiterals
  // Constructs the object passed to the tag function in a tagged
  // template literal.
  taggedTemplateLiteralLoose: function (strings, raw) {
    // Babel's own version of this calls Object.freeze on `strings` and
    // `strings.raw`, but it doesn't seem worth the compatibility and
    // performance concerns.  If you're writing code against this helper,
    // don't add properties to these objects.
    strings.raw = raw;
    return strings;
  },

  // es6.classes
  // Checks that a class constructor is being called with `new`, and throws
  // an error if it is not.
  classCallCheck: function (instance, Constructor) {
    if (!(instance instanceof Constructor)) {
      throw new TypeError("Cannot call a class as a function");
    }
  },

  // es6.classes
  inherits: function (subClass, superClass) {
    if (typeof superClass !== "function" && superClass !== null) {
      throw new TypeError("Super expression must either be null or a function, not " + typeof superClass);
    }

    if (superClass) {
      if (Object.create) {
        // All but IE 8
        subClass.prototype = Object.create(superClass.prototype, {
          constructor: {
            value: subClass,
            enumerable: false,
            writable: true,
            configurable: true
          }
        });
      } else {
        // IE 8 path.  Slightly worse for modern browsers, because `constructor`
        // is enumerable and shows up in the inspector unnecessarily.
        // It's not an "own" property of any instance though.
        //
        // For correctness when writing code,
        // don't enumerate all the own-and-inherited properties of an instance
        // of a class and expect not to find `constructor` (but who does that?).
        var F = function () {
          this.constructor = subClass;
        };
        F.prototype = superClass.prototype;
        subClass.prototype = new F();
      }

      // For modern browsers, this would be `subClass.__proto__ = superClass`,
      // but IE <=10 don't support `__proto__`, and in this case the difference
      // would be detectable; code that works in modern browsers could easily
      // fail on IE 8 if we ever used the `__proto__` trick.
      //
      // There's no perfect way to make static methods inherited if they are
      // assigned after declaration of the classes.  The best we can do is
      // to copy them.  In other words, when you write `class Foo
      // extends Bar`, we copy the static methods from Bar onto Foo, but future
      // ones are not copied.
      //
      // For correctness when writing code, don't add static methods to a class
      // after you subclass it.
      for (var k in superClass) {
        if (hasOwn.call(superClass, k)) {
          subClass[k] = superClass[k];
        }
      }
    }
  },

  createClass: (function () {
    var hasDefineProperty = false;
    try {
      // IE 8 has a broken Object.defineProperty, so feature-test by
      // trying to call it.
      Object.defineProperty({}, 'x', {});
      hasDefineProperty = true;
    } catch (e) {}

    function defineProperties(target, props) {
      for (var i = 0; i < props.length; i++) {
        var descriptor = props[i];
        descriptor.enumerable = descriptor.enumerable || false;
        descriptor.configurable = true;
        if ("value" in descriptor) descriptor.writable = true;
        Object.defineProperty(target, descriptor.key, descriptor);
      }
    }

    return function (Constructor, protoProps, staticProps) {
      if (! hasDefineProperty) {
        // e.g. `class Foo { get bar() {} }`.  If you try to use getters and
        // setters in IE 8, you will get a big nasty error, with or without
        // Babel.  I don't know of any other syntax features besides getters
        // and setters that will trigger this error.
        throw new Error(
          "Your browser does not support this type of class property.  " +
            "For example, Internet Explorer 8 does not support getters and " +
            "setters.");
      }

      if (protoProps) defineProperties(Constructor.prototype, protoProps);
      if (staticProps) defineProperties(Constructor, staticProps);
      return Constructor;
    };
  })(),

  // es7.objectRestSpread and react (JSX)
  _extends: Object.assign || (function (target) {
    for (var i = 1; i < arguments.length; i++) {
      var source = arguments[i];
      for (var key in source) {
        if (hasOwn.call(source, key)) {
          target[key] = source[key];
        }
      }
    }
    return target;
  }),

  // es6.destructuring
  objectWithoutProperties: function (obj, keys) {
    var target = {};
    outer: for (var i in obj) {
      if (! hasOwn.call(obj, i)) continue;
      for (var j = 0; j < keys.length; j++) {
        if (keys[j] === i) continue outer;
      }
      target[i] = obj[i];
    }
    return target;
  },

  // es6.destructuring
  objectDestructuringEmpty: function (obj) {
    if (obj == null) throw new TypeError("Cannot destructure undefined");
  },

  // es6.spread
  bind: Function.prototype.bind || (function () {
    var isCallable = function (value) { return typeof value === 'function'; };
    var $Object = Object;
    var to_string = Object.prototype.toString;
    var array_slice = Array.prototype.slice;
    var array_concat = Array.prototype.concat;
    var array_push = Array.prototype.push;
    var max = Math.max;
    var Empty = function Empty() {};

    // Copied from es5-shim.js (3ac7942).  See original for more comments.
    return function bind(that) {
      var target = this;
      if (!isCallable(target)) {
        throw new TypeError('Function.prototype.bind called on incompatible ' + target);
      }

      var args = array_slice.call(arguments, 1);

      var bound;
      var binder = function () {

        if (this instanceof bound) {
          var result = target.apply(
            this,
            array_concat.call(args, array_slice.call(arguments))
          );
          if ($Object(result) === result) {
            return result;
          }
          return this;
        } else {
          return target.apply(
            that,
            array_concat.call(args, array_slice.call(arguments))
          );
        }
      };

      var boundLength = max(0, target.length - args.length);

      var boundArgs = [];
      for (var i = 0; i < boundLength; i++) {
        array_push.call(boundArgs, '$' + i);
      }

      // Create a Function from source code so that it has the right `.length`.
      // Probably not important for Babel.  This code violates CSPs that ban
      // `eval`, but the browsers that need this polyfill don't have CSP!
      bound = Function('binder', 'return function (' + boundArgs.join(',') + '){ return binder.apply(this, arguments); }')(binder);

      if (target.prototype) {
        Empty.prototype = target.prototype;
        bound.prototype = new Empty();
        Empty.prototype = null;
      }

      return bound;
    };

  })()
};