title: Array becomes an Integer after applying unshift on it
body: <p>I have an Object like this:</p>
  
  <pre><code>{
    "index": 0,
    "name": "b1a042ff6-0c75-4af2-a9da-1a16f333baee_p0",
    "category": "others",
    "rawUrl": "https://firebasestorage.googleapis.com/v0/b/vrcam-dev-5a815.appspot.com/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&amp;token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
    "isTopLogo": false,
    "origin": "https://firebasestorage.googleapis.com/v0/b/vrcam-dev-5a815.appspot.com/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&amp;token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
    "position": {
      "x": 0,
      "y": 0
    },
    "panoramaRotation": {
      "x": 0,
      "y": 0,
      "z": 0
    }
  }
  </code></pre>
  
  <p>Which I want to <code>unshift</code> to an Array (it's cloned version) like this:</p>
  
  <pre><code>[{
    "adjustedRawUrl": "",
    "category": "others",
    "createdAt": 1514432540000,
    "cubemapReady": false,
    "desktopUrl": "https://im.ages.io/BGOLielt?cors&amp;w=513",
    "floorplanRotation": 0,
    "index": 0,
    "is720": false,
    "isTopLogo": false,
    "mobileUrl": "https://im.ages.io/BGOLielt?cors&amp;w=4096",
    "name": "b1a042ff6-0c75-4af2-a9da-1a16f333baee_p0",
    "objectId": "3c312986-0ef1-42fc-9068-46fc13a04b8f",
    "panoramaRotation": {
      "x": 0,
      "y": 0,
      "z": 0
    },
    "position": {
      "x": 0,
      "y": 0
    },
    "rawUrl": "https://firebasestorage.googleapis.com/v0/b/vrcam-dev-5a815.appspot.com/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_lPea0mIc6H.png?alt=media&amp;token=9e1494ff-2525-42a6-a058-12c26560349a",
    "stereoUrl": "",
    "thumbnail": "https://im.ages.io/BGOLielt?cors&amp;w=400",
    "updatedAt": 1514432619000
  }, {
    "adjustedRawUrl": "",
    "category": "others",
    "createdAt": 1514432231000,
    "cubemapReady": false,
    "desktopUrl": "https://im.ages.io/FK9uiel2?cors&amp;w=251",
    "floorplanRotation": 0,
    "index": 1,
    "is720": false,
    "isTopLogo": false,
    "mobileUrl": "https://im.ages.io/FK9uiel2?cors&amp;w=4096",
    "name": "b1a042ff6-0c75-4af2-a9da-1a16f333baee_p0",
    "objectId": "08e9197c-ab27-48d8-a48d-b33452fcfd11",
    "panoramaRotation": {
      "x": 0,
      "y": 0,
      "z": 0
    },
    "position": {
      "x": 0,
      "y": 0
    },
    "rawUrl": "https://firebasestorage.googleapis.com/v0/b/vrcam-dev-5a815.appspot.com/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_pMUnnhYmpH.png?alt=media&amp;token=e422e4f1-389b-43b7-927b-022b31e37d61",
    "stereoUrl": "",
    "thumbnail": "https://im.ages.io/FK9uiel2?cors&amp;w=400",
    "updatedAt": 1514432619000
  }]
  </code></pre>
  
  <p>This is how I'm doing it:</p>
  
  <pre><code>const newClonedArray = JSON.parse(JSON.stringify(array)).unshift(object)
  </code></pre>
  
  <p>To my shock the result wasn't an Array but an Integer: <code>3</code>.</p>
  
  <p>Why is this? And how to fix it?</p>