You can translate JavaScript to Python using Js2Py. It supports whole JavaScript and you can use it to translate large JavaScript modules like esprima.js (a JavaScript 6 parser).

>>> import js2py
>>> f = js2py.eval_js( "function $(a) {return a + arguments[1]}" )
>>> f
function $(a) { [python code] }
>>> f(1, 2, 3)
3

This is how the translated function looks like internally (it's rather ugly):

>>> print js2py.translate_js( "function $(a) {return a + arguments[1]}" )
from js2py.pyjs import *
var = Scope( JS_BUILTINS )
set_global_object(var)
# Code follows:
var.registers([u'$'])
@Js
def PyJsHoistedNonPyName(a, this, arguments, var=var):
    var = Scope({u'a':a, u'this':this, u'arguments':arguments}, var)
    var.registers([u'a'])
    return (var.get(u'a')+var.get(u'arguments').get(u'1'))
PyJsHoistedNonPyName.func_name = u'', PyJsHoistedNonPyName)

You can actually run a Python interpreter directly in JS thanks to emscripten.

The project is called empythoned:

Empythoned is a build script that uses Emscripten to compile CPython for use in a browser. It attempts to compile the main interpreter as a single small executable and the whole standard library as dynamically loaded libraries.

but be warned:

The project is in its infancy. Right now the core interpreter works very well, but many of the libraries either don't work at all or contain various bugs.