JavaScript interpreter in Python
Python JavaScript
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jspy - JavaScript interpreter in Python

jspy is a toy JavaScript interpreter in Python created by Marek Stepniowski. Its implementation is directly based on ECMA-262 standard (PDF).


First install the package:

    $ cd /main/jspy/folder
    $ python install

You may need to have root rights, depending on your system configuration. After the installation, jspy script should be on your path. You can then just run the script with the JavaScript file as a single argument:

    $ jspy file.js

Test suite

To run the test suite, you either need Python 2.7 or the unittest2 package installed.

Python < 2.7:

    $ cd /main/jspy/folder
    $ unit2 discover

Python >= 2.7:

    $ cd /main/jspy/folder
    $ python -m unittest discover

Source code

You can find the newest source code of jspy on GitHub.

Implemented features

  • Expressions (excluding delete, typeof, instanceof and in operators)
  • Statements (excluding for and for in loops, with, switch, labels and exception handling)
  • Functions (with nested execution scopes allowing for closures)
  • Basic object support (Object and Array literals, item assignment)
  • console.log, same as in Node.js and Firebug

Todo (in order of priorities)

  • for and for in loops
  • switch statement
  • Full object support (including an Array implementation)
  • delete, typeof, instanceof and in operators
  • Function statements
  • Sane error messages
  • Prototypal inheritance
  • Exception handling
  • Strict mode (should we run in strict mode by default?)
  • Proper value behaviour (right now the behaviour of Number and String objects is Python-like and can sometimes be different than in JavaScript)
  • Automatic semicolon insertion (as defined in section 7.9 of ECMA-262)
  • Labels for break and continue statements
  • with statement (it's evil!)


The code is released open-source under the MIT license. See license.txt file for details.