#こうする
function Clazz() {
let hoge = "hogehoge";
this.setHoge = function(param) {
hoge = param;
};
this.getHoge = function() {
return hoge;
};
}
const a = new Clazz();
const b = new Clazz();
a.setHoge("ほげほげ")
console.log(a.getHoge()); // ほげほげ
console.log(b.getHoge()); // hogehoge
console.log(a.hoge); // undefined