Comma operator in constructor can cause "out of order" property initialization #937

It seems that under some circumstances where property initialization in a constructor is done with chained comma operators (a common result of minified code), the obfuscator can cause out of order initialization, where later initializations in the chain don't have access to previous initializations.

Minimal working example that will help to reproduce issue

class BuggyClass {
  constructor(param1, param2) {
    (this.param1 = param1),
      (this.param2 = param2),
      (this.obj = {
        param1: this.param1,
        param2: this.param2,
      });
  }

  debug() {
    console.log("BUGGY CLASS");
    console.log({ obj: this.obj });
    console.log({ param1: this.param1, param2: this.param2 });
  }
}

class GoodClass {
  constructor(param1, param2) {
    (this.param1 = param1),
      (this.param2 = param2),
      (this.obj = {
        param1: this.param1,
        param2: param2,
      });
  }

  debug() {
    console.log("GOOD CLASS");
    console.log({ obj: this.obj });
    console.log({ param1: this.param1, param2: this.param2 });
  }
}

const buggyClass = new BuggyClass("param1", "param2");

buggyClass.debug();

const goodClass = new GoodClass("param1", "param2");

goodClass.debug();

And obfuscated with these options:

    target: "node",
    optionsPreset: "medium-obfuscation",
    disableConsoleOutput: false,

Expected Behavior

The expected console output (and what you get when you run the file without obfuscation) is:

BUGGY CLASS
{ obj: { param1: 'param1', param2: 'param2' } }
{ param1: 'param1', param2: 'param2' }
GOOD CLASS
{ obj: { param1: 'param1', param2: 'param2' } }
{ param1: 'param1', param2: 'param2' }

The object here has the values from the previously initialized properties.

Current Behavior

BUGGY CLASS
{ obj: { param1: undefined, param2: undefined } }
{ param1: 'param1', param2: 'param2' }
GOOD CLASS
{ obj: { param1: 'param1', param2: 'param2' } }
{ param1: 'param1', param2: 'param2' }

Here, the obj object, has the fields undefined, despite coming after the initialization of those properties. Unexpectedly, in the GoodClass, the parameters are set correctly. The only difference between the classes is that the GoodClass uses param2: param2, rather than param2: this.param2 when initializing obj. I'm not sure what's going on internally that makes this work propertly, but it might be helpful.

Steps to Reproduce

You can use the above setup. I've also made a proof of concept repo, where you can demonstrate the bug with:

yarn
node build.js && node done.js

Your Environment

• Obfuscator version used: 2.15.1
• Node version used: 14.17.0