Javascript groupBy实现仅生成1组

function groupBy(array, key) {
  return array.reduce(function(acc, obj) {
    let groupKey = obj[key];
    if (!acc[groupKey]) {
      acc[groupKey] = [];
    }
    acc[groupKey].push(obj);
    return acc;
  }, {});
}

const students = [
  { name: 'Alice', grade: 'A' },
  { name: 'Bob', grade: 'B' },
  { name: 'Charlie', grade: 'A' },
  { name: 'Dave', grade: 'C' },
  { name: 'Eve', grade: 'B' }
];

const groupedStudents = groupBy(students, 'grade');
console.log(groupedStudents);

{
  A: [
    { name: 'Alice', grade: 'A' },
    { name: 'Charlie', grade: 'A' }
  ],
  B: [
    { name: 'Bob', grade: 'B' },
    { name: 'Eve', grade: 'B' }
  ],
  C: [
    { name: 'Dave', grade: 'C' }
  ]
}