Updating values of an object within array

Question

I have an array of objects that looks like this:

[
   {
      "id": 123,
      "timeStamp": "\"2019-07-08T20:36:41.580Z\"",
      "data": [1, 2, 3]
   },
   {
      "id": 234,
      "timeStamp": "\"2019-07-08T20:37:12.472Z\"",
      "data": ["Apples", "Oranges"]
   }
]

I want to update the value of a particular property of an object within the array but also want to make sure that I return the result in a new array.

How do I do this without running through some type of a loop e.g. for loop?

Say, I want to update the data property of the second object and add Bananas to it.

You will need some kind of loop to iterate through your array: it will be either explicit or implicit. — PM 77-1
– PM 77-1, Commented Jul 8, 2019 at 20:47
You're going to need to loop through this array one way or another if you want to keep them in array form, unless you keep track of the index of each object in the array, at which point you're just using an object with extra steps. — ldtcoop
– ldtcoop, Commented Jul 8, 2019 at 20:47

Michael Beeson · Accepted Answer · 2019-07-08 20:52:07Z

2

If you want the result to be a new array, you'll first have to clone the array. This can be more complicated than you might imagine (depending on how deeply you wish to clone things). One way is to use JSON stringify...

Bear in mind that the JSON trick is effectively doing a loop behind the scenes. Inevitable if you want to copy the array, really.

To find the object by ID use Array.find()

let original = [
   {
      "id": 123,
      "timeStamp": "\"2019-07-08T20:36:41.580Z\"",
      "data": [1, 2, 3]
   },
   {
      "id": 234,
      "timeStamp": "\"2019-07-08T20:37:12.472Z\"",
      "data": ["Apples", "Oranges"]
   }
]

let copy = JSON.parse(JSON.stringify(original));

copy.find(obj => obj.id === 234).data.push("Bananas");

console.log(copy);

edited Jul 8, 2019 at 20:52

answered Jul 8, 2019 at 20:46

Michael Beeson

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7 Comments

Sam Over a year ago

This is very very close to what I want but I may not always know the index of the object I want to update.

Michael Beeson Over a year ago

Well how do you plan on identifying the object you wish to modify? By id?

Sam Over a year ago

I'd like to use the id property to identify the object that I need to update

Michael Beeson Over a year ago

See the edit I've made – you can use Array.find to get the first element in an array that has a specific id (here I set the id to 234 but presumably id will be a variable passed to a function)

Sam Over a year ago

Excellent! Thank you! I assume changing the value is simply an assignment e.g. copy.find(obj => obj.id === 234).timeStamp = JSON.stringify(new Date());

|

Sdpotts93 · Accepted Answer · 2019-07-08 20:47:49Z

0

Something like this would do the trick:

 let arr = [
    {
     "id": 123,
     "timeStamp": "\"2019-07-08T20:36:41.580Z\"",
     "data": [1, 2, 3]
    },
    {
     "id": 234,
     "timeStamp": "\"2019-07-08T20:37:12.472Z\"",
     "data": ["Apples", "Oranges"]
     }
  ]

 arr[1]['data'] = [...arr[1]['data'], 'Bananas']

 console.log(arr)

answered Jul 8, 2019 at 20:47

Sdpotts93

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1 Comment

PM 77-1 Over a year ago

"... but also want to make sure that I return the result in a new array."

Abhishek Jain · Accepted Answer · 2019-07-08 20:48:23Z

-1

For your example: you can do something like this: say your array of object is saved in test variable

test[1].data.push("Bananas")

answered Jul 8, 2019 at 20:48

Abhishek Jain

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1 Comment

PM 77-1 Over a year ago

Does not answer OP question at all.

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