How does Python call JS?

from ： Micro reading   https://www.weidianyuedu.com

1. Preface

daily Web In the process of end crawler , We often encounter scenarios where parameters are encrypted , therefore , We need to analyze the web page source code

Pass mode , Layer by layer, the key JS Code , Use  Python  To execute this code , Get the parameters before and after encryption  Python  Realization

This article will talk about the use of  Python call JS Of 4 Ways of planting

2. Get ready

In a simple  JS The script, for example , Write the code to a file

//norm.js// Calculate the sum of two numbers function add(num1, num2) {    return num1 + num2;}

among , Defines a method , Calculate the sum of two numbers

3. Mode one ：PyExecJSPyExecJS It's the most used way , The underlying implementation is ： In the local JS Operation in environment JS Code supported JS Environment contains ：Node.js、PyV8、PhantomJS、Nashorn Wait first , We need to install dependency packages  PyExecJS

//py_exec_js_demo.py// Installation dependency pip3 install PyExecJS

then , from JS Read the source code from the file

def js_from_file(file_name):    """     Read js file     :return:    """    with open(file_name, "r", encoding="UTF-8") as file:        result = file.read()    return result

Last , Use execjs Class compile() Method to compile and load the above JS character string , Returns a context object

import execjsfrom js_code import *#  Compile load js character string context1 = execjs.compile(js_from_file("./norm.js"))

Last , Call the of the context object call()  Method execution JS Method among them , Parameters include ：JS The name of the method whose code is called 、 The incoming parameters of the corresponding method

#  call js In code add() Method , Parameter is 2 and 3#  Method name ：add#  Parameters ：2 and 3result1 = context1.call("add", 2, 3)print(result1)

Need to pay attention to , because  PyExecJS  Run locally JS In the environment , It will start before use JS Environmental Science , Eventually, the running speed will be slow. For more functions, please refer to ：https://github.com/doloopwhile/PyExecJS

4. Mode two ：js2pyjs2py As a pure Python Realized JS Interpreter , Can be completely detached from JS Environmental Science , Direct will JS Code conversion to Python Code first , Install dependency library

#  Install dependency library pip3 install js2py

And then use js2py Medium EvalJs() Method to generate a context object

#  Use to get up and down js2py Generate a context context = js2py.EvalJs()

Then use the context object to execute JS Script , Convert to  Python Code

#  Execute whole paragraph JS Code context.execute(js_content)

Last , Use context to call JS The method in , And make input parameters

#  Use context context Call specific functions #  Function name ：add#  Parameters ：1,2result = context.add(1, 2)print(result)

It's important to note that , If JS It's a long confusing code , Convert to Python The process may report an error

More functions can be found in ：

https://github.com/PiotrDabkowski/Js2Py

5. Mode three ：Node.js

It's actually using Python Of os.popen perform node command , perform JS Script

First , Make sure that... Is installed locally Node.js Environmental Science

modify JS Script , Add an export function init , It is convenient for internal functions to be called

// Calculate the sum of two numbers function add(num1, num2) {    return num1 + num2;}// Add an export function （node The way ）module.exports.init = function (arg1, arg2) {    // Call function , And back to     console.log(add(arg1, arg2));};

then , Will call JS  Method to form a string

#  Composition call js The order of # node command ：node -ecmd = "node -e "require(\\"%s\\").init(%s,%s)"" % ("./norm", 3, 5)

Last , adopt os.popen Just execute the order

pipeline = os.popen(cmd)#  Read the results result = pipeline.read()print(" The result is :", result)

6. Mode 4 ：PyV8

PyV8 yes Google  take Chrome V8  lead m.weidianyuedu.com Engine use Python Encapsulated dependency Libraries

It does not rely on local JS Environmental Science , Very fast

import PyV8from js_code import js_from_filewith PyV8.JSContext() as ctx:    ctx.eval(js_from_file("./norm.js"))#  call js function , Specify the parameters ctx.locals.add(1, 2)

But after repeated tests, it was found that ,MAC and PC stay Python3 In the environment , Use PyV8 Will report all kinds of strange questions , So... Is not recommended ！

More functions can be found in ：

https://github.com/emmetio/pyv8-binaries

7. Last

It's summarized above Python call JS Of 4 Ways of planting

In the actual crawler project , It's usually used first node Command a test , After making sure there's no problem , Before reuse 3 In any of these ways Python rewrite .