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JSEngine is a simple wrapper of Javascript engines.

Project description


This is a simple wrapper of Javascript engines, it wraps the Javascript interpreter for Python use.

There are two ways to call interpreters, via dynamic library loading is internal call which is faster than the other one, via subprocess is external call.

  • System's built-in Javascript interpreter:

    macOS: JavascriptCore
    Linux: Gjs on Gnome, CJS on Cinnamon, etc.
    Windows: Chakra (internal call, but not applicable to Windows 7)

  • Python bindings (Recommend, internal call):

    PyMiniRacer (V8) (Caused by a scope issue, its work process is similar to external call now, to fix the scope issue, Esprima is needed)

  • Any installed external Javascript interpreters, e.g.

    SpiderMonkey, Node.js, QuickJS, etc.

JSEngine used to be part of YKDL, which created by @coslyk.


Install from version package format monthly downloads

pip install jsengine

Or download and Install from source code

python install


  • Python >= 2.7


import jsengine
jsengine.eval('"Hello, world!"')  # => 'Hello, world!'

Use a JSEngine context.

    ctx1 = jsengine.jsengine()
except jsengine.RuntimeError:
    ...  # do something if useless

if jsengine.JSEngine is None:
    ...  # do something if useless
    ctx2 = jsengine.JSEngine("""
            function add(x, y) {
                return x + y;

ctx1.eval('1 + 1')  # => 2

# call funtion"add", 1, 2)  # => 3

# append new script
    function square(x) {
        return x ** 2;
    """)"square", 9)  # => 81

Use a specified external Javascript interpreter.

binary = binary_name or binary_path
kwargs = {
    'name': 'None or any string',  # see ExternalInterpreterNameAlias.keys()
    'tempfile': True,              # use tempfile or not. Default is False, fallback is True
    'evalstring': True,            # can run command string as Javascript or can not,
                                   # just like '-e script_code'
                                   # instead of True, supported argument can be passed,
                                   # e.g. '--eval', '--execute'
    'args': [args1, args2, ...]    # arguments used for interpreter

# case 1
interpreter = jsengine.ExternalInterpreter.get(binary, **kwargs)
if interpreter:
    # found
    ctx = jsengine.ExternalJSEngine(interpreter)

# case 2
if jsengine.set_external_interpreter(binary, **kwargs):
    # set default external interpreter OK
    ctx = jsengine.ExternalJSEngine()

# case 3, maybe get default fallback instead of your specified
    ctx = jsengine.ExternalJSEngine(interpreter=binary, **kwargs)
except jsengine.RuntimeError:
    ...  # do something if useless

Use threading lock. Javascript source itself always be ran in single threaded, that just make the APIs can be used in multithreadeding.

jsengine.set_threading(True)   # MUST enable befor using, it's disabled by default

ctx_quickjs = jsengine.QuickJSEngine()
ctx_chakra = jsengine.ChakraJSEngine()   # internal chakra will create an extra thread per context
ctx_v8 = jsengine.V8JSEngine()
ctx_exter = jsengine.ExternalJSEngine()  # external interpreter will be called one by one with context

...  # do multithreading

jsengine.set_threading(False)  # disable is not necessary

Internal VS. External

QuickJSEngine ChakraJSEngine V8JSEngine (esprima) V8JSEngine ** ExternalJSEngine
Load backend on import import or init init init every fetch result
Loading speed fastest fast very slow with py3 fast very slow
Performance highest high low, if much results low, if much results
Fetch result run the passed run the passed run the passed run all/full source run all/full source

* Fetch results means call eval()/call().
** V8JSEngine is now similar to ExternalJSEngine which caused by scope issue.


JSEngine is released under the MIT License.

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