修改数组对象的属性名（只修改对象的key，不修改value）

let arr = [ { name: '张三', year: 18}, { name: '李四', year: 19}] 
let brr = [ { userName: '张三', age: 18}, { userName: '李四', age: 19} ]

changeKeys (arr, key) {
  let newArr = [];
  arr.forEach(item => {
    let obj = {};
    for (var i = 0; i < key.length; i++) {
      obj[key[i]] = item[Object.keys(item)[i]]
    }
    newArr.push(obj);
  })
  return newArr;
}
 
let brr= changeKeys (arr, ['userName', 'age']);