query.js

const listPosts = `query listPosts(
  $filter: ModelPostFilterInput
  $limit: Int
  $nextToken: String
) {
  listPosts(filter: $filter, limit: $limit, nextToken: $nextToken) {
    items {
      id
      user_id
      title
      body
      createdAt
    }
  }
}`;

const { data } = await API.graphql(
  graphqlOperation(listPosts, {
    user_id: {
      eq: 10
    }
  })
);