How to run JavaScript in Python

JavaScript and Python are two of the most popular and commonly used languages ​​in the world. JavaScript is an integral part of his web development, both front-end and back-end. Python, on the other hand, is suitable for back-end coding and rapid application development.

Both have their advantages, but running JavaScript code from a Python program gives you the best of both worlds.

An introduction to JavaScript and its syntax

JavaScript is a scripting language used for web development. You can use JavaScript to add behavior and functionality to your web pages. It is an interpreted language, which means the code is executed in real time without a compiler translating it into machine language.

Some of the language’s unique syntactic features are:

1. Code block: JavaScript uses curly braces ({}) to enclose statements within the same block.
2. variable: can be used to define variables. variable keyword. The syntax for initializing variables is: var variable name = value;.
3. constantYou can use : to define constants. constant keyword. The syntax for defining constants is const constant name = value;.
4. operator: There are many logical operators available in JavaScript. &&, || When !The . equality operator has two forms: == compare the values ​​and === Compare values ​​and data types.
5. Input/output: You can receive input in JavaScript using window.prompt() Display the output to the console using console.log().

Whether you’re considering full-stack, front-end, or back-end development, you need to understand the basics of JavaScript.

Python syntax

Python is a high-level programming language with applications in back-end development, artificial intelligence, and data science. Python is considered a dynamically typed, garbage collected, interpreted language.

Here are some important syntaxes to look out for in Python:

1. Code block: Python uses indentation to enclose statements within the same block.
2. variable: You can initialize variables in Python like this: variable name = value.
3. incessant: Python doesn’t really support constants, but convention dictates that variables should be named in uppercase and should not be changed. CONSTANT_NAME.
4. operator: You can use logical operators like When, Also,and No. using the equality operator (==) Compare both values ​​and types of data.
5. Input/output: You can get input from the user using input() View the output using printing().

Python is one of the easiest languages ​​to master and definitely needs to get your hands dirty if you want to use it for a wide range of applications. These courses and apps are the best places to learn Python for free.

What is a Js2Py module?

Js2Py is a JavaScript to Python translator and JavaScript interpreter written in 100% pure Python by Piotr Dabkowski. To install this module, open a terminal and run:

 pip install js2py 

Js2Py automatically converts valid JavaScript (ECMA Script 5.1, ECMA 6) to Python without using any dependencies. Uses only standard Python libraries.

As stated in the official GitHub documentation, there are three limitations to using Js2Py modules.

1. Js2py ignores strict mode.
2. of When statement is not supported.
3. Handles indirect calls to . evaluation as a direct call to Evaluate.

Despite these limitations, the module is fully functional and translates most JavaScript code into the Python language.

Example of running JavaScript code in Python

Here are some examples of translating and running JavaScript code in Python.

1. Hello World Program

The first program you write in any language is the Hello World program. Implement like this:

 import js2py
js2py.eval_js('console.log("Hello World!")') 

The first step is the import js2py Add the module to your environment. JavaScript code as a parameter eval_js() Rate it. Passing console.log(“Hello World!”) will print Hello World! In the Python output terminal, just like in your browser’s console window.

2. A function that adds two numbers

Here’s how to perform addition of two numbers using JavaScript in Python.

 import js2py
js_add = '''function add(a, b){
return a + b;
}'''
add = js2py.eval_js(js_add)
print(add(3, 7)) 

Declare a function using the JavaScript style and enclose it in a multi-line string (“”” or ”’), which can be stored in a variable called . js_add. Pass the function variable to eval_js() Translate it to the Python equivalent. Display the result by making a function call and passing two numbers as arguments.

This is the output from adding two numbers using a JavaScript function.

3. How to convert an entire JavaScript file to a Python file

Suppose you have a JavaScript file named . example.js It contains the following code:

 
function Rectangle(w, h) {
  this.w = w;
  this.h = h
}
Rectangle.prototype = {
  getArea: function () {
    return this.w * this.h
  }
};
x = new Rectangle(10, 5) 

This JavaScript contains a function Rectangle that takes width and height as parameters and returns the area calculated using the formula width * height.

There are two easy ways to convert JavaScript files to Python files. they are:

1. The first method runs the JavaScript file without explicit translation. You can implement it like this:

    import js2py
   eval_result, example = js2py.run_file('example.js') 

   of run_file() It takes a JavaScript file as an argument and returns the result of evaluation along with an object that you can use to run and test your JS code.

2. The second method is to explicitly convert the entire JavaScript file and save it to a Python file. You can implement it like this:

    import js2py
   js2py.translate_file('example.js', 'example.py') 

   The first method allows you to work with JavaScript files in the Python environment itself. However, if you just want to convert the file and run it in Python, the second method is better.

4. Creating objects using the new function

Objects in JavaScript files cannot be created as follows: new example.Rectangle(8,2)Instead, you should use .new(8,2). can be coded as follows:

 import js2py
eval_result, example = js2py.run_file('example.js')
rect = example.Rectangle.new(8,2)
print(rect.getArea()) 

Convert a JavaScript file containing code to calculate the area of ​​a rectangle using the first method.use Dot (.) operator to access rectangle Use the function inside the evaluated file, new() A function that creates that object. Pass two numbers as arguments.use getArea() Calculate and display area using functions. Print statement.

This is the output obtained for calculating the area of ​​a rectangle using JavaScript.

Running Python in your browser

Python is a popular tool for coding on the backend, but there are some tools you can try on the frontend as well. You can use Brython, Transcrypt, and Pyjs to create JavaScript-powered web applications entirely in Python.

You can use other strategies to combine Python code and JavaScript in the same application. The easiest is to communicate via a simple, open standard like JSON.