Using Map function inside of another Map function in React Js

I want to add genre to my Movie Search app's carousel using map function. I have two json files one of them is an array of movie data as objects having a key as genre_ids eg:
genre_ids:
0: 16
1: 28
2: 12
3: 35
4: 10751
5: 14


and other contains an array of objects specifying the name of the genre with a unique key. eg:
{
"genres": [
{
"id": 10759,
"name": "Action & Adventure"
}
]
}

The Json files:

1. Movie data: https://api.themoviedb.org/3/trending/all/day?api_key=921345714956c7d9c3db36ac3f20ee09
2. Genre: https://api.themoviedb.org/3/genre/movie/list?api_key=921345714956c7d9c3db36ac3f20ee09&language=en-US

I tried mapping the json with movie data first. Then while mapping the genre i checked if the id of the genre matches with that of the id of the movie data element. Then I returned the name of that particular genre. But it is returning the names of all the genre present in the genre json.

My code:

{
  trend.map((e, i) => {
    return (
      <div className="carousel-item" key={i}>
        <img
          src={`${img}${e.backdrop_path}`}
          className="d-block carimage" alt="..." />
        <div className="carousel-caption d-none d-md-block">
          <div className='caro-discription'>
          <button className='trailer-main-button'>More Info!!</button>
          <h1>{e.title?e.title:e.name}</h1>
          <h3>Rating: {e.vote_average}/10</h3>
          </div>
          <div className='genre-list'> 
          {genre.map((a,b)=>{
            return(
            <h3 className='genre-list-item' key={b}>{a.id=e.genre_ids? a.name: null}</h3>
            )
          })}
          </div> 
        </div>
      </div>


    )
  })
}

Change

<h3 className='genre-list-item' key={b}>{a.id=e.genre_ids? a.name: null}</h3>

to

<h3 className='genre-list-item' key={b}>{a.id===e.genre_ids? a.name: null}</h3>

There are a couple of things you're doing wrong here. First is the use of map instead of find. Your Movie object has one genre_ids property which is always a positive integer. This means what you don't need to map all genres which match the genre_ids, instead you just need to find the specific genre your movie is tagged as:

<h3 key={e.genre_ids * e.id}>{genres.find((g, idx) => g.id === e.genre_ids).name}</h3>

If you do have multiple genres, then you'd use map:

{genres.map((g, idx) => e.genre_ids.includes(g.id) ? <h3 key={e.id * g.id}>{g.name}</h3> : null )}

This way you save processing time.
Also, your code has the issue of using = for comparison. A single equals sign is used for assignment. If you want to check equality between two values, you'd use ==. If you want to check if the two are of the same type as well, you'd use ===.