ES7特性
Array.prototype.includes
从此不用再写myArr.indexOf(value) > -1，而只需要用myArr.includes(value)即可
Rest/spread properties
let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
x; // 1
y; // 2
z; // { a: 3, b: 4 }
Decorators 装饰器
function readonly(target, name, descriptor){
descriptor.writable = false;
return descriptor;
}
class Person {
@readonly
name() { return `${this.first} ${this.last}` }
}