Python runs JavaScript code using execjs module

In programming, Python and JavaScript are two widely used programming languages. Python is known for its simplicity and powerful library support, while JavaScript is the main force in web development. If you have ever encountered a situation in a Python project where JavaScript code needs to be run, then there is a very convenient solution - use the execjs module! Today we will explore in-depth how to run JavaScript code in Python through this module to make your project more powerful!

1. Why do you need to run JavaScript in Python

Before we start, let's first explore why JavaScript code may be required to run in Python. Common scenarios include:

Processing JavaScript API response: Some web services and APIs return content requires JavaScript to be executed to generate the final result.

Reuse existing JavaScript code: If you already have a piece of code logic written in JavaScript and don't want to rewrite its Python version.

Analysis and rendering of dynamic content: During Web Scraping, the content of some pages is dynamically generated through JavaScript.

2. Introduction to execjs module

execjs is a Python library that provides an interface to execute JavaScript code. It can automatically select and call the JavaScript runtime environment (such as, JScript, etc.) in the system, thereby executing JavaScript code in the Python environment.

To use execjs, you need to install it first. You can install this module through pip:

pip install PyExecJS

After installing execjs, we will learn how to run JavaScript code in Python.

3. How to use the execjs module to run JavaScript code

Let's start with some basic examples and learn how to run JavaScript code in Python using execjs.

1. Basic usage

First, we need to import the execjs module and use it to run a simple JavaScript code:

import execjs
 
# JavaScript Codejs_code = """
function add(a, b) {
    return a + b;
}
"""
 
# Load JavaScript codectx = (js_code)
 
# Call functions in JavaScriptresult = ("add", 1, 2)
 
print("1 + 2 =", result)  # Output: 1 + 2 = 3

In this example, we define a simple JavaScript function add, compile it through the() method, and then use the() method to directly call the JavaScript function.

2. Use external JavaScript files

If your JavaScript logic is more than a few words, saving it in a separate file may be more in line with your needs. Execjs can also handle this situation.

import execjs
 
# Read external JavaScript fileswith open("", "r") as f:
    js_code = ()
 
# Load JavaScript codectx = (js_code)
 
# Call functions in JavaScriptresult = ("yourFunctionName", "arg1", "arg2")

Here we read external JavaScript files through Python file operations, and then use execjs to compile and run the functions in it.

3. Advanced usage: Capture JavaScript output and errors

When executing JavaScript code, we may also need to capture output and error messages. execjs makes this simple and straightforward.

import execjs
 
# JavaScript Codejs_code = """
function divide(a, b) {
    if (b === 0) {
        throw new Error("Division by zero");
    }
    return a / b;
}
"""
 
ctx = (js_code)
 
try:
    # Try to call a function in JavaScript    result = ("divide", 4, 0)
except  as e:
    print("An error occurred:", e)

In this example, we define a divide function and deliberately pass zero as a divisor to cause an error, and catch the error through try-except and handle it.

4. Runtime environment management of execjs module

execjs can use multiple JavaScript runtime environments. You can view the available runtime environments in the following ways:

import execjs
 
# View supported runtimesprint(().name)

If you have multiple JavaScript runtimes in your system, such as JScript, you can specify which one to use:

import execjs
 
# Set to runtimectx = (execjs.runtime_names.Node)

5. Frequently Asked Questions and Debugging

When using execjs, you may encounter the following common problems:

JavaScript runtime is not available: Make sure that the system has JScript, or other JavaScript engines installed.

JavaScript syntax error: Check whether the syntax of JavaScript code is correct.

Function Undefined: Ensure that the called function is defined in the JavaScript environment after().

When encountering problems, debugging can be done by checking error messages and ensuring that the JavaScript environment is configured correctly.

6. Summary

With the execjs module, we can easily run JavaScript code in Python. Whether it is simple function calls or handling complex JavaScript logic, execjs can meet your needs. This capability allows you to reuse existing JavaScript code in Python projects, process dynamic content, and enhance cross-language collaboration, providing great flexibility and convenience.

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