js如何修改对象数组的key值

//原数据
dataOld: [{ count: '33', area: '122.2', districtId: 43000 }, { count: '44', area: '168.2', districtId: 43001 }] 
//接口需要的数据
dataNew: [{ countAll: '33', countArea: '122.2', districtId: 43000 }, { count: '44', area: '168.2', districtId: 43001 }]

let dataNew = [];    //新数组
dataOld.map(item => {
    let obj = {
        countAll: item.count,
        countArea: item.area,
        districtId: item.districtId,
    }
     dataNew.push(obj);
});

let dataNew = [];    //新数组
dataOld.map(item => {
    let _item = JSON.parse(JSON.stringify(item).replace('count', 'countAll').replace('area', 'countArea'));
    dataNew.push(_item)
});

convertKey (arr, key) {
    let dataNew = []; //新数组
    this.dataOld.forEach((item, index) => {
        let obj = {}; //新数组里的新对象
        for (var i = 0; i < key.length; i++) {
            obj[key[i]] = item[Object.keys(item)[i]]; //key值替换  
        }
        dataNew.push(obj);
    })
    console.log(dataNew,'dataNew');
    return dataNew;
},
                                            // 改变后的key
let dataNew = this.convertKey(this.dataOld, ['countAll', 'countArea', 'districtId']);