SOURCE

//----------extends 可以用来继承类 还可以继承原生类------------//
class VersionedArray extends Array{
    constructor(){
        super();
        this.history=[[]];
    }
    commit(){
        this.history.push(this.slice());
    }
    revert(){
        this.splice(0,this.length,...this.history[this.history.length-1]);
        //从0 删除到最后一个元素. 然后插入上一个版本的元素 (其实是一个数组)
    }
}

let x=new VersionedArray();
x.push(1);
x.push(2);
console.log(x);
console.log(x.history);

x.commit();
console.log(x.history);

x.push(3);
console.log(x);
console.log(x.history);

x.revert();
console.log(x);
console.log(x.history);