Create an array of objects with values from another object

I have an object looking like this

const item = {
  id: 123,
  type: 'book',
  sections: [{
    type: 'section',
    id: '456',
    index: 1,
    lessons: [{
      type: 'lesson',
      id: 789,
      index: 1
    },
    {
      type: 'lesson',
      id: 999,
      index: 2
    }
    ]
  }, {
    type: 'section',
    index: 2,
    id: 321,
    lessons: [{
      type: 'lesson',
      id: 444,
      index: 1
    },
    {
      type: 'lesson',
      id: 555,
      index: 2
    }
    ]
  }]
}

It should be assumed that there are more objects in sections and lessons array. I want to create a new object like this

result = [{
  section: 456,
  lessons: [789, 999]
}, {
  section: 321,
  lessons: [444, 555]
}]

I tried this loop but this just pushes indexes and not lesson’s ids

let obj = {};
let sectionWithLessons = [];
let lessons = []

for (const i in item.sections) {
  obj = {
    sectionId: item.sections[i].id,
    lessonIds: item.sections[i].lessons.map((lesson) => {
      return lessons.push(lesson.id)
    }),
  };
  sectionWithLessons.push(obj);
}

console.log(sectionWithLessons);

How can i do this correctly and preferably with good performance in consideration?

>Solution :

I believe the best/shortest thing is to use the map function, like:

const result2 = item.sections.map(({id, lessons}) => ({
  id, 
  lessons: lessons.map(({id: lessionId}) => lessionId)
}))