如何通过嵌套在对象数组的属性中的对象属性的值在对象数组中找到多个索引？

Question

I have an array of objects, each object has a property of "watched" that is an array of objects by itself.

let arr = 
        [ 
            {   
                id: 1, 
                name: "A", 
                watched: [ 
                            {movieId: 7, movieName: "Avatar"} , 
                            {movieId: 8, movieName: "Titanic"}
                        ]
            },
            {   
                id: 2, 
                name: "B", 
                watched: [   
                            {movieId: 1, movieName: "Armageddon"} , 
                            {movieId: 8, movieName: "Titanic"}
                        ]
            },
            {   
                id: 3, 
                name: "C", 
                watched: [   
                            {movieId: 1, movieName: "Armageddon"} , 
                            {movieId: 7, movieName: "Avatar"}
                        ]
            }

        ]

I need an array of indexes according to a given MovieId. If I want an array of indexes who watched movieId no. 7 (Avatar) - I'll get:

let AvatarWatchers = [0,2]

I tried:

AvatarWatchers = arr.filter((item) => item.watched.find(movieObj => movieObj.movieId == 7) > -1 )

But It's not working and I'm getting an empty array.

Answer 1

 let arr = [ { id: 1, name: "A", watched: [ {movieId: 7, movieName: "Avatar"} , {movieId: 8, movieName: "Titanic"} ] }, { id: 2, name: "B", watched: [ {movieId: 1, movieName: "Armageddon"} , {movieId: 8, movieName: "Titanic"} ] }, { id: 3, name: "C", watched: [ {movieId: 1, movieName: "Armageddon"} , {movieId: 7, movieName: "Avatar"} ] } ]; let result = arr.map((item, index) => ({...item, index})) .filter(item => item.watched.find(watchedItem => watchedItem.movieName === 'Avatar')) .map(item => item.index); console.log('expected result', result);