javascript - Array becomes an Integer after applying unshift on it - Stack Overflow

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I have an Object like this:

{
  "index": 0,
  "name": "b1a042ff6-0c75-4af2-a9da-1a16f333baee_p0",
  "category": "others",
  "rawUrl": ".appspot/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
  "isTopLogo": false,
  "origin": ".appspot/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
  "position": {
    "x": 0,
    "y": 0
  },
  "panoramaRotation": {
    "x": 0,
    "y": 0,
    "z": 0
  }
}

Which I want to unshift to an Array (it's cloned version) like this:

[{
  "adjustedRawUrl": "",
  "category": "others",
  "createdAt": 1514432540000,
  "cubemapReady": false,
  "desktopUrl": ";w=513",
  "floorplanRotation": 0,
  "index": 0,
  "is720": false,
  "isTopLogo": false,
  "mobileUrl": ";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": ".appspot/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_lPea0mIc6H.png?alt=media&token=9e1494ff-2525-42a6-a058-12c26560349a",
  "stereoUrl": "",
  "thumbnail": ";w=400",
  "updatedAt": 1514432619000
}, {
  "adjustedRawUrl": "",
  "category": "others",
  "createdAt": 1514432231000,
  "cubemapReady": false,
  "desktopUrl": ";w=251",
  "floorplanRotation": 0,
  "index": 1,
  "is720": false,
  "isTopLogo": false,
  "mobileUrl": ";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": ".appspot/o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_pMUnnhYmpH.png?alt=media&token=e422e4f1-389b-43b7-927b-022b31e37d61",
  "stereoUrl": "",
  "thumbnail": ";w=400",
  "updatedAt": 1514432619000
}]

This is how I'm doing it:

const newClonedArray = JSON.parse(JSON.stringify(array)).unshift(object)

To my shock the result wasn't an Array but an Integer: 3.

Why is this? And how to fix it?

I have an Object like this:

{
  "index": 0,
  "name": "b1a042ff6-0c75-4af2-a9da-1a16f333baee_p0",
  "category": "others",
  "rawUrl": "https://firebasestorage.googleapis./v0/b/vrcam-dev-5a815.appspot./o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
  "isTopLogo": false,
  "origin": "https://firebasestorage.googleapis./v0/b/vrcam-dev-5a815.appspot./o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
  "position": {
    "x": 0,
    "y": 0
  },
  "panoramaRotation": {
    "x": 0,
    "y": 0,
    "z": 0
  }
}

Which I want to unshift to an Array (it's cloned version) like this:

[{
  "adjustedRawUrl": "",
  "category": "others",
  "createdAt": 1514432540000,
  "cubemapReady": false,
  "desktopUrl": "https://im.ages.io/BGOLielt?cors&w=513",
  "floorplanRotation": 0,
  "index": 0,
  "is720": false,
  "isTopLogo": false,
  "mobileUrl": "https://im.ages.io/BGOLielt?cors&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./v0/b/vrcam-dev-5a815.appspot./o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_lPea0mIc6H.png?alt=media&token=9e1494ff-2525-42a6-a058-12c26560349a",
  "stereoUrl": "",
  "thumbnail": "https://im.ages.io/BGOLielt?cors&w=400",
  "updatedAt": 1514432619000
}, {
  "adjustedRawUrl": "",
  "category": "others",
  "createdAt": 1514432231000,
  "cubemapReady": false,
  "desktopUrl": "https://im.ages.io/FK9uiel2?cors&w=251",
  "floorplanRotation": 0,
  "index": 1,
  "is720": false,
  "isTopLogo": false,
  "mobileUrl": "https://im.ages.io/FK9uiel2?cors&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./v0/b/vrcam-dev-5a815.appspot./o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_pMUnnhYmpH.png?alt=media&token=e422e4f1-389b-43b7-927b-022b31e37d61",
  "stereoUrl": "",
  "thumbnail": "https://im.ages.io/FK9uiel2?cors&w=400",
  "updatedAt": 1514432619000
}]

This is how I'm doing it:

const newClonedArray = JSON.parse(JSON.stringify(array)).unshift(object)

To my shock the result wasn't an Array but an Integer: 3.

Why is this? And how to fix it?

• javascript
• arrays

Share Improve this question Follow asked Dec 28, 2017 at 3:47 alexalex 7,6111515 gold badges5353 silver badges7979 bronze badges

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2 Answers 2

Sorted by: Reset to default 12

array.unshift() returns length of the modified array. It does not create a new array instead modifies the existing array. Thus you do not need to use any assignment here.

var object ={
  "index": 0,
  "name": "b1a042ff6-0c75-4af2-a9da-1a16f333baee_p0",
  "category": "others",
  "rawUrl": "https://firebasestorage.googleapis./v0/b/vrcam-dev-5a815.appspot./o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
  "isTopLogo": false,
  "origin": "https://firebasestorage.googleapis./v0/b/vrcam-dev-5a815.appspot./o/5ab4f2a0-88e9-4bf5-86b5-61b528be707f/panoramas/panorama_XTsagLoxbA.png?alt=media&token=68ef261e-0c5e-4bf0-aebc-ab845fcec01a",
  "position": {
    "x": 0,
    "y": 0
  },
  "panoramaRotation": {
    "x": 0,
    "y": 0,
    "z": 0
  }
}

var array = [];

array.unshift(object);

console.log(array);

The docs explain

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

Maybe instead of assigning the result of unshift, do

const newClonedArray = JSON.parse(JSON.stringify(array));
newClonedArray.unshift(object);

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