Get keys out of array of objects : Javascript

Question

I have this scenario where I need to fetch only the keys in an array of objects. Object structure is shown below. I have also tried an approach but it does not seem like working. Can someone help me out with this.

var arr = [
        { firstName: "aaaaa", status: 0, visits: 155 },
        { firstName: "aabFaa", status: 0, visits: 155 },
        { firstName: "adaAAaaa", status: 10, visits: 1785 },
        { firstName: "aAaaaa", status: 50, visits: 175 },
        { firstName: "aaaaa", status: 670, visits: 155 },
      ]

console.log([...new Set(arr.map(item => Object.keys(item)))]); //  This does not work

I want the output to be just ['firstName','status','visits']

What doe you expect the result to be?

Bergi
– Bergi

2019-06-23 18:35:03 +00:00
Commented Jun 23, 2019 at 18:35 — Bergi
– Bergi, Commented Jun 23, 2019 at 18:35

Bergi · Accepted Answer · 2019-06-23 18:36:34Z

6

Object.keys does itself return an array, so your map creates an array of arrays. Use flatMap instead:

console.log(Array.from(new Set(arr.flatMap(Object.keys))))

Alternatively, since all objects in your array have the same keys, you could just take those of the first object:

console.log(Object.keys(arr[0]))

(this also makes it obvious that the code only works on non-empty arrays)

answered Jun 23, 2019 at 18:36

Bergi

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adiga · Accepted Answer · 2019-06-23 18:42:15Z

2

You are trying to create a Set from a 2D array of keys. Use flatMap to get a flattened array of keys of all the objects in the array

[...new Set(arr.flatMap(item => Object.keys(item)))]

Here's a snippet:

const arr = [
      { firstName: "aaaaa", status: 0, visits: 155 },
      { firstName: "aabFaa", status: 0, visits: 155 },
      { firstName: "adaAAaaa", status: 10, visits: 1785 },
      { firstName: "aAaaaa", status: 50, visits: 175 },
      { firstName: "aaaaa", status: 670, visits: 155 },
    ];
    
const uniqueKeys = [...new Set(arr.flatMap(Object.keys))]

console.log(uniqueKeys)

edited Jun 23, 2019 at 18:42

answered Jun 23, 2019 at 18:36

adiga

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2 Comments

georg Over a year ago

Could be just flatMap(Object.keys)

adiga Over a year ago

@georg yeah. I just copied OP's code. And, Bergi has already suggested that.

connexo · Accepted Answer · 2019-06-23 18:39:51Z

1

Object.keys(arr[0]) is probably the shortest solution, assuming each object in arr has the same keys:

var arr = [{
    firstName: "aaaaa",
    status: 0,
    visits: 155
  },
  {
    firstName: "aabFaa",
    status: 0,
    visits: 155
  },
  {
    firstName: "adaAAaaa",
    status: 10,
    visits: 1785
  },
  {
    firstName: "aAaaaa",
    status: 50,
    visits: 175
  },
  {
    firstName: "aaaaa",
    status: 670,
    visits: 155
  },
]

let keys = Object.keys(arr[0]);

console.log(keys);

answered Jun 23, 2019 at 18:39

connexo

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