>>59 class Base { getThis(): Base { return this; } } class Derived extends Base { print(): void { console.log('Derived'); } } let derived = new Derived(); derived.getThis().print(); // 1.6.2だとBaseにprint()がねーよと怒られる 1.7だと getThis(): this { return this; } にする事でコンパイル通ってちゃんと実行も出来る