diff --git a/youtube_dl/jsinterp/jsbuilt_ins.py b/youtube_dl/jsinterp/jsbuilt_ins.py
new file mode 100644
index 000000000..c5aac82fc
--- /dev/null
+++ b/youtube_dl/jsinterp/jsbuilt_ins.py
@@ -0,0 +1,60 @@
+from __future__ import unicode_literals
+
+
+class JSBase(object):
+    def __init__(self, cls=None):
+        if cls is None:
+            cls = self.__class__
+
+        if cls is JSBase:
+            self.prototype = {}
+        else:
+            super(cls, self).__init__(cls.__bases__[0])
+            self.prototype.update(cls.prototype)
+
+    def get_proto_prop(self, prop):
+        return self.prototype[prop](self)
+
+
+class JSObject(JSBase):
+    def __init__(self, value=None):
+        super(JSObject, self).__init__()
+        self.value = value
+        self.props = {}
+
+    @staticmethod
+    def get_prototype_of(o):
+        return 'prototype'
+
+    def has_own_prop(self):
+        return 'object has own prop'
+
+    def to_string(self):
+        return 'object to string'
+
+    prototype = {'hasOwnProperty': has_own_prop, 'toLocaleString': to_string}
+    props = {'prototype ': prototype, 'getPrototypeOf': get_prototype_of}
+
+
+class JSArray(JSObject):
+
+    def __init__(self, length=0):
+        super(JSArray, self).__init__()
+        self.value = []
+        self.props = {'length': length}
+
+    @staticmethod
+    def is_array(arg):
+        return 'is array'
+
+    def concat(self):
+        return 'concat'
+
+    def join(self):
+        return 'join'
+
+    def to_string(self):
+        return 'array to string'
+
+    prototype = {'concat': concat, 'join': join, 'toLocaleString': to_string}
+    props = {'prototype ': prototype, 'isArray': is_array, 'length': 1}