Run Obfuscated JavaScript Directly in Python with ExecJS – A Quick Guide

Introduction

In web scraping, Python is the dominant language, but many sites protect data with JavaScript obfuscation, making it hard to extract values directly.

Why Execute JavaScript from Python?

Anti‑scraping measures often rely on client‑side JavaScript, especially obfuscated code that generates dynamic data. Re‑implementing the logic in Python is tedious, so being able to run the original JS and obtain its return value simplifies the process.

What Is JavaScript Code Obfuscation?

Normal Code

The following simple function returns a formatted date string.

function formatDate(now) {
    var now = new Date(1230999938);
    var year=now.getFullYear();
    var month=now.getMonth()+1;
    var date=now.getDate();
    var hour=now.getHours();
    var minute=now.getMinutes();
    var second=now.getSeconds();
    return year+"-"+month+"-"+date+" "+hour+":"+minute+":"+second;
}

Running this code produces the expected date output.

Obfuscated Code

After passing the same function through an online obfuscator, the code becomes unreadable but still functional.

function formatDate(mz1){var KkkGDiH2=new window["\x44\x61\x74\x65"](1230999938);var tsk3=KkkGDiH2['\x67\x65\x74\x46\x75\x6c\x6c\x59\x65\x61\x72']();var YMreyP4=KkkGDiH2['\x67\x65\x74\x4d\x6f\x6e\x74\x68']()+1;var Ozo5=KkkGDiH2['\x67\x65\x74\x44\x61\x74\x65']();var QMYEc$eD6=KkkGDiH2['\x67\x65\x74\x48\x6f\x75\x72\x73']();var JfXVV_Akq7=KkkGDiH2['\x67\x65\x74\x4d\x69\x6e\x75\x74\x65\x73']();var $mP8=KkkGDiH2['\x67\x65\x74\x53\x65\x63\x6f\x6e\x64\x73']();return tsk3+"\x2d"+YMreyP4+"\x2d"+Ozo5+" "+QMYEc$eD6+"\x3a"+JfXVV_Akq7+"\x3a"+$mP8

Even though the code is heavily obfuscated, it can still be executed and returns the same result.

Python Package ExecJS

ExecJS is a Python library that provides a simple interface to run JavaScript code using an installed JavaScript runtime such as Node.

Installation

pip3 install PyExecJS

Running JavaScript from Python

Example with a straightforward function:

import execjs

ctx = execjs.compile("""
function add(x, y) {
  return x + y;
}
""")
print(ctx.call("add", 1, 2))

Executing Obfuscated JavaScript

The same approach works with obfuscated code:

import execjs

ctx = execjs.compile("""
function add(bi1,Pl$2){return bi1+Pl$2}
""")
print(ctx.call("add", 1, 2))

Thus, even heavily obfuscated JavaScript can be executed from Python without de‑obfuscation.

Conclusion

Anti‑scraping techniques will continue to evolve, but tools like ExecJS allow Python developers to run JavaScript directly, turning a difficult obstacle into a straightforward solution.