const lodash = require('lodash');
const select = ['_id','username','email','sex'];
const selectQur = lodash.reduce(select, function (result, value, key) {
    result[value] = 1;
    return result;
},{});

{
  $project: {
     _id: 1,
     username: 1,
     email: 1,
     sex: 1
  }
}