nestedloop.js

function setContent() {
  url = data[user_index].pictures[pic_index].url;
  document.getElementById('dog_image').src = url;
}

function next () {
  pics_in_user = data[user_index].pictures.length;
  if (pic_index === pics_in_user-1) {
    pic_index = 0;
    if (user_index === data.length-1) {
      alert('This is the end');
    } else {
      user_index = user_index + 1;
    }
  } else {
    pic_index = pic_index + 1;
  };
  setContent();
};

function previous () {
  pics_in_user = data[user_index].pictures.length;
  if (pic_index === 0) {
    if (user_index === 0) {
      alert('This is the beginning');
    } else {
      user_index = user_index - 1;
    }

  } else {
    pic_index = pic_index - 1;
  }
  setContent();
};

function setProgress() {
  pics_in_user = data[user_index].pictures.length;
  
}

var data = [
  {
    "id": 1,
    "name": "name1",
    "pictures": [
      {
        "id": 1,
        "url": "https://images.dog.ceo/breeds/retriever-golden/n02099601_7588.jpg"
      },
      {
        "id": 2,
        "url": "https://images.dog.ceo/breeds/beagle/n02088364_17294.jpg"
      }
    ]
  },
  {
    "id": 2,
    "name": "name2",
    "pictures": [
      {
        "id": 3,
        "url": "https://images.dog.ceo/breeds/coonhound/n02089078_353.jpg"
      },
      {
        "id": 4,
        "url": "https://images.dog.ceo/breeds/springer-english/n02102040_3006.jpg"
      }
    ]
  }
];

var user_index = 0;
var pic_index = 0;

url = data[0].pictures[0].url;
document.getElementById('dog_image').src = url;
document.getElementById('progress').style.width = '10px';