JS’s classes cannot be used correctly in python

[zanxueyan]

Issue type

Bug

How did you install PythonMonkey?

Installed from pip

OS platform and distribution

Windows 11

Python version (python --version)

3.10

PythonMonkey version (pip show pythonmonkey)

0.2.1

Bug Description

When python calls js, it is not possible to modify the properties of a class through its methods.

consult:How to instantiate JS's classes in python?

Standalone code to reproduce the issue

//JS code
class Runoob {
  constructor(name, url) {
    this.name = name;
    this.url = url;
  }
  setname(name)
  {
      this.name = name;
      console.log("box");
      return this.name;
  }
}
//first Type:transmit the class
module.exports = Runoob

//secend Type: Create an instance pass an instance
pepole = new Runoob("ddd","www.baidu.com")

************
#python code


import pythonmonkey as pm

pep =pm.require("./pyreadjs")
#first Type Error:TypeError: class constructors must be invoked with 'new'

pep("ddd","www.baidu.com")
# but can't code like this:
#test = new pep("ddd","www.baidu.com")

print(pep.setname("test")) #can return OK
print(pep.name)     #NOT CHANGE

Relevant log output or backtrace

pythonmonkey.SpiderMonkeyError: TypeError: class constructors must be invoked with 'new'

Additional info if applicable

No response

What branch of PythonMonkey were you developing on? (If applicable)

No response

[wiwichips]

Hi @zanxueyan , thank you so much for taking the time to play with PythonMonkey and submit this issue!

Since Python lacks a new keyword for instantiating objects, we had to add a new(class) function to the PythonMonkey API. Here's a small example:

import pythonmonkey as pm
jsDateClass = pm.Date
myDate = pm.new(jsDateClass)(0) # in js this would be: let myDate = new Date(0);

---

Here's the change you would need to make to get your code working

//JS code
class Runoob {
  constructor(name, url) {
    this.name = name;
    this.url = url;
  }
  setname(name)
  {
      this.name = name;
      console.log("box");
      return this.name;
  }
}
//first Type:transmit the class
module.exports = Runoob

//secend Type: Create an instance pass an instance
pepole = new Runoob("ddd","www.baidu.com")

#python code


import pythonmonkey as pm

Runoob =pm.require("./pyreadjs")
#first Type Error:TypeError: class constructors must be invoked with 'new'

pep = pm.new(Runoob)("ddd","www.baidu.com")
# but can't code like this:
#test = new pep("ddd","www.baidu.com")

print(pep.setname("test")) #can return OK
print(pep.name)     #NOT CHANGE

Running the python program results in the following output:

box
test
ddd

I changed a couple things in your python code here:

1. Runoob = pm.require("./pyreadjs")

• Get the JS class from pyreadjs.js

2. pep = pm.new(Runoob)("ddd","www.baidu.com")

• Instantiate a new Runoob and set a variable pep equal to it. I'm using the pm.new(Class)(args...) function to instantiate a new object

---

I'm sorry you had this experience, we'll try to improve the error message or improve the documentation so more people don't run into this in the future. Thank you!!!

[zanxueyan]

Thanks a lot！

[zanxueyan]

`import pythonmonkey as pm

Runoob = pm.require("./pyreadjs") # Get the JS class from pyreadjs.js

pep = pm.new(Runoob)("ddd", "www.baidu.com") # Instantiated object
print(pep.add(2, 3))
pep.setname("test")
print(pep.name) # You cannot get the value of the property directly in this way
##Whether you can support getting its value from an attribute???

print(pep.getname()) # You need to use the built-in function to get the value`

[wiwichips]

Hi @zanxueyan Good catch!!! - you're right, something is wrong here...

import pythonmonkey as pm

Runoob = pm.require("./pyreadjs") # Get the JS class from pyreadjs.js

pep = pm.new(Runoob)("Will Pringle", "www.google.com") # Instantiated object
pep.setname("Joseph")

print(pep['name'])   # prints Will Pringle BUT SHOULD PRINT Joseph
print(pep.name)      # prints Will Pringle BUT SHOULD PRINT Joseph
print(pep.getname()) # prints Joseph

I'll file a bug report - thank you so much for finding and reporting this error!

[wiwichips]

@zanxueyan check this out: #172 (comment)

seems to be another side effect of this bug - I'll notify you when we have it patched

---

import pythonmonkey as pm

pm.eval("""
class Human {
  constructor(name)
  {
    this.name = name;
  }

  setName(name)
  {
    this.name = name;
  }

  getName()
  {
    return this.name;
  }
}

""")

Human = pm.eval('Human')

person = pm.new(Human)('Will')

# setting it using setName
person.setName('Joe')

print(person.getName()) # prints "Joe"
print(person.name) # prints "Will" but should print "Joe"!!!
print(person['name']) # prints "Will" but should print "Joe"!!!

# now try setting it directly 
person.name = "Liang"

print(person.getName()) # prints "Joe"
print(person.name) # prints "Liang"!!!
print(person['name']) # prints "Liang"!!!

prints

Joe
Will
Will
Joe
Liang
Liang

[zanxueyan]

@wiwichips Thank you very much! Are there any further optimization results at present? Looking forward to...

[wiwichips]

This should be solved in the next release of PythonMonkey - not sure when that is - but I'll make sure to notify you @ zanxueyan