数组结构转为对象?

let arr = [
  { num: '2', text: 'aaa', quantity: 1 },
  { num: '1', text: 'bbb', quantity: 2 },
  { num: '2', text: 'ccc', quantity: 1 },
  { num: '2', text: 'ddd', quantity: 1 },
  { num: '1', text: 'eee', quantity: 1 }
];

let obj = {};

// 遍历数组并将条目按照num属性值分组
arr.forEach(item => {
  const num = item.num;
  const answer = item.text;
  const quantity = item.quantity;
  
  if (!obj[num]) {
    obj[num] = [];
  }
  
  obj[num].push({ answer, quantity });
});

// 输出结果
console.log(obj);