Examples of classes, constructors, instantiation, and "this" keyword.

Node.js

class Foo {
  constructor(value) {
    this.item = value;
  }

  getItem() {
    return this.item;
  }

  setItem(value) {
    this.item = value;
  }
}

const foo = new Foo("bar");
console.log(foo.item);

foo.setItem("qux");

const item = foo.getItem();
console.log(item);

Output

bar
qux

Go

(closest thing to a class is to use a structure)

package main

import "fmt"

type Foo struct {
	Item string
}

func NewFoo(value string) *Foo {
	return &Foo{
		Item: value,
	}
}

func (f *Foo) GetItem() string {
	return f.Item
}

func (f *Foo) SetItem(value string) {
	f.Item = value
}

func main() {
	foo := NewFoo("bar")
	fmt.Println(foo.Item)

	foo.SetItem("qux")

	item := foo.GetItem()
	fmt.Println(item)
}

Output

bar
qux