JSFiddle - React, Tailwind, and code Playground

JavaScript

var prop = {
  number:1
}

class Test {
  constructor(prop) {
    this.prop = prop
  }
}

var testInstance = new Test(prop)
prop.number = 2
console.log(testInstance.prop.number) //2 ????

/*
hoisting:
class Test {
  constructor(prop) {
    this.prop = prop
  }
}
var prop = undefined
var testInstance = undefined
prop = {
  number:1
}
prop.number = 2
testInstance = new Test(prop)
*/