query-2.js

'use strict';

Array.prototype.concatAll = function() {
  var results = [];
  this.forEach(function(subArray) {
    if (Array.isArray(subArray))
      subArray.forEach((item) => results.push(item))
    else
      throw new Error('Its not two dimensional array;');
  });

  return results;
};


function queryNestedArray() {
  var movieLists = [{
      name: "New Releases",
      videos: [{
        "id": 70111470,
        "title": "Die Hard",
        "rating": 4.0
      }, {
        "id": 654356453,
        "title": "Bad Boys",
        "rating": 5.0
      }]
    }, {
      name: "Dramas",
      videos: [{
        "id": 65432445,
        "title": "The Chamber",
        "rating": 4.0
      }, {
        "id": 675465,
        "title": "Fracture",
        "rating": 5.0
      }]
    }],
    allVideoIdsInMovieLists = [];

  return movieLists.map(movieList =>
      movieList.videos.map(video =>
        video.id
      ) // [id, id]
    ) // [[id, id], [id, id]]
    .concatAll(); // [id, id, id, id]
}

console.log(queryNestedArray()); // [70111470, 654356453, 65432445, 675465]