vuejs - mapState object rest spread

refer to: https://vuex.vuejs.org/zh/guide/state.html

https://github.com/tc39/proposal-object-rest-spread

let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
x; // 1
y; // 2
z; // { a: 3, b: 4 }