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Run JavaScript code from Python

Project description


Run JavaScript code from Python.

PyExecJS is a porting of ExecJS from Ruby. PyExecJS automatically picks the best runtime available to evaluate your JavaScript program.

A short example:

>>> import execjs
>>> execjs.eval("'red yellow blue'.split(' ')")
['red', 'yellow', 'blue']
>>> ctx = execjs.compile("""
...     function add(x, y) {
...         return x + y;
...     }
... """)
>>>"add", 1, 2)

Supported runtimes


$ pip install PyExecJS


$ easy_install PyExecJS


If EXECJS_RUNTIME environment variable is specified, PyExecJS pick the JavaScript runtime as a default:

>>> execjs.get().name # this value is depends on your environment.
>>> os.environ["EXECJS_RUNTIME"] = "Node"
>>> execjs.get().name
'Node.js (V8)'

You can choose JavaScript runtime by execjs.get():

>>> default = execjs.get() # the automatically picked runtime
>>> default.eval("1 + 2")
>>> jscript = execjs.get("JScript")
>>> jscript.eval("1 + 2")
>>> node = execjs.get("Node")
>>> node.eval("1 + 2")

The pros of PyExecJS is that you do not need take care of JavaScript environment. Especially, it works in Windows environment without installing extra libraries.

One of cons of PyExecJS is performance. PyExecJS communicate JavaScript runtime by text and it is slow. The other cons is that it does not fully support runtime specific features.

PyV8 might be better choice for some use case.


Copyright (c) 2016 Omoto Kenji. Copyright (c) 2011 Sam Stephenson and Josh Peek. (As a author of ExecJS)

Released under the MIT license. See LICENSE for details.



  • Supported Python 3.5
  • Supported Nashorn(Java 8 JavaScript engine) as runtime
  • Dropped support for Python 2.6 and 3.2


  • Supported Python 3.4
  • Supported SlimerJS as runtime
  • Supported PhantomJS as runtime
  • Fixed JScript runtime on Windows 8


  • Supported Python 3.3
  • Fixed file handle leaking
  • Fixed issue with passenger-nginx-4.0


  • Removed “import execjs” (it prevent execution of by Python 2.6)


  • Javascript sources were embeded in ‘which’ command were reimplemented by pure python.


  • Python 2.6.x was supported.


  • Forgotten shell=True was added to Popen.


  • First release.

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