code: function classCall(func, object, staticObject, superClass) {
    if (superClass) {
      return parseExpression
          `($traceurRuntime.createClass)(${func}, ${object}, ${staticObject},
                                         ${superClass})`;
    }
    return parseExpression
        `($traceurRuntime.createClass)(${func}, ${object}, ${staticObject})`;
  }
docs: Maximally minimal classes  http://wiki.ecmascript.org/doku.php?id=strawman:maximally_minimal_classes  This transforms class declarations and class expressions.  class C extends B { constructor(x) { super(); } method() { super.m(); } }  =>  var C = function(x) { $__superCall(this, $C.prototype, 'constructor', []); }; var $C = $traceurRuntime.createClass(C, { method: function() { $traceurRuntime.superCall(this, $C.prototype, 'm', []); } }, {}, B);