class limitArray extends Array{
    constructor(maxNum){
        super()
        Object.defineProperty(this,"maxNum",{
            enumerable:false,//是否可以被枚举
            value:maxNum,
            writable:true
        });
    }
    push(item){
        Array.prototype.unshift.call(this,item)
        if(this.length>this.maxNum){
            Array.prototype.pop.call(this)
        }
    }
}
module.exports=limitArray;