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

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

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

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

# call funtion
ctx2.call("add", 1, 2)  # => 3

# append new script
ctx1.append("""
    function square(x) {
        return x ** 2;
    }
    """)
ctx1.call("square", 9)  # => 81

binary = binary_name or binary_path
kwargs = {
    'name': 'None or any string',  # see ExternalInterpreterNameAlias.keys()
    'tempfile': True,              # use tempfile or not
    'evalstring': True,            # can run command string as Javascript
                                   # or can not, '-e script_code'
    '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
try:
    ctx = jsengine.ExternalJSEngine(interpreter=binary, **kwargs)
except jsengine.RuntimeError:
    ...  # do something if useless