如何将通过条件查询得到的res中以某一字段为关键字遍历出来的数据赋值给新的数组？

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如何将通过条件查询得到的res中以某一字段为关键字遍历出来的数据赋值给新的数组？How to assign the data traversed by a certain field as the key in res obtained by conditional query to a new array?

Query the cloud database to get a res array, and print the data and length of the array in the debugging interface. The print result is: 51 lines are res; 52 lines are res res.data ; 53 yes res.data.length What I want to achieve is to res.data The data traversed by using the seathao field as the keyword is assigned to the new array as the data of the next picker, but every time or this.setdata Assignment is not successful, ask big guys to point out!!!

回答：

[{  a: 1,  b: 2}, {  a: 3,  b: 4}].map(item => {  return item.a})// [1, 3]