How to Call a JavaScript Function from Python Code

This post will demonstrate how to execute JavaScript in Python using the PythonMonkey library for Python.

Refer to the PythonMonkey docs for more advanced features: https://docs.pythonmonkey.io/

Installation

Installing PythonMonkey is easy, you’ll just need to have npm and python installed on your system. Then install PythonMonkey using pip

$ pip install pythonmonkey

Example #1: Calling JavaScript Functions from Python

We’ll use the eval() function from PythonMonkey to evaluate JavaScript code in this example. It runs JavaScript code in a context and makes the functions, variables, etc available through pythonmonkey.gloablThis

import pythonmonkey as pm

# a string containing some javascript functions
my_js_code = """
function adder(a,b) {
  return a + b;
}

function subtracter(a,b) {
  return a - b;
}
"""

# put your javascript string inside pm.eval to execute it
pm.eval(my_js_code)

# call the adder function from Python
print(pm.globalThis.adder(1,2)) # outputs 3
print(pm.globalThis.adder(99,1)) # outputs 100

# call the subtracter function from Python
print(pm.globalThis.subtracter(1,2)) # outputs -1
print(pm.globalThis.subtracter(99,1)) # outputs 98

Example #2: Calling JavaScript Functions in another File from Python

In this example, we’ll use the require() function from PythonMonkey to load a JavaScript module into Python and call functions from it. This is just like how you would load a module in Node.js, but it works in Python!

In this example, we’ll use two files simple-math.js and main.py. The main.py Python script will call the JavaScript functions in simple-math.js.

main.py:

from pythonmonkey import require as js_require

js_lib = js_require('./simple-math')

print(js_lib.add(1,2)) #  3
print(js_lib.sub(1,2)) # -1

simple-math.js

function add(a,b) {
  return a + b;
}

function sub(a,b) {
  return a - b;
}

// We'll define the exports object just like in Node.js / npm modules
module.exports = {
  add,
  sub,
}

Then, if we execute main.py by typing $ python3 main.py we’ll get our results:

3

-1

I hope you found this article useful, here are some additional PythonMonkey resources you may find helpful:

• YouTube tutorial: https://www.youtube.com/watch?v=UmlSryXsh30

Consider giving PythonMonkey a star on GitHub to support it! (https://github.com/Distributive-Network/PythonMonkey)!