activated:function(){
    this.getData()
},
data() {
    return {
        dataList:[]
    };
},
mounted() {
    console.log(this.dataList[0]) //undefined
},
methods: {
    getData() {
        for (var i = 1; i < 20; i++) {
            this.dataList.push(i)
        }
        console.log(this.dataList[0]) //1
    },
},

這是什么原因？