javascript cannot map array of objects with nested values

Question

Trying to map array of objects with values nested in child objects structure like:

const objs = [{
        "B": {
            "value": 1,
        },
        "D": {
            "value": "45"
        },
        "E": {
            "value": "234"
        },
        "A": {
            "value": "543"
        },
        "C": {
            "value": "250"
        }
    },...]

to the structure like:

[
  { name: 'B', value: 1 }, 
  { name: 'D', value: '45' }, 
  { name: 'E', value: '234' }, 
  { name: 'A', value: '543' },
  { name: 'C', value: '250' }
]

and the result of the mapping is undefined

const mapped = objs.map((key, index) => {
  Object.keys(key).map(el => ({
    name: el
  }))
})

Example: Stackblitz

return is missing.

random
– random

2019-07-16 11:55:18 +00:00
Commented Jul 16, 2019 at 11:55 — random
– random, Commented Jul 16, 2019 at 11:55

antonku · Accepted Answer · 2019-07-16 12:07:10Z

5

You are missing return statement and value property definition.

Besides you may want to use flatMap instead of map in order to avoid a nested array in the result:

const objs = [{
    "B": {
        "value": 1,
    },
    "D": {
        "value": "45"
    },
    "E": {
        "value": "234"
    },
    "A": {
        "value": "543"
    },
    "C": {
        "value": "250"
    }
}]

const mapped = objs.flatMap((key, index) => {
    return Object.keys(key).map(el => ({
        name: el,
        value: key[el].value
    }))
})

console.log(mapped)

edited Jul 16, 2019 at 12:07

answered Jul 16, 2019 at 11:59

antonku

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2 Comments

corry Over a year ago

Great example. Is there a way to keep order of the elements through the iteration as in the example?

antonku Over a year ago

Thanks! Is the order of objects in result different from the order of keys? On my side it appear to be the same (B, D, E, A, C).

Iiskaandar · Accepted Answer · 2019-07-16 12:04:14Z

4

You should operate on objs[0], not objs, because it is an array of one object, not array of objects.

let array = []
for(let object in objs[0]){
array.push({
"name": object,
"value": objs[0][object].value
})
}

answered Jul 16, 2019 at 12:04

Iiskaandar

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1 Comment

corry Over a year ago

My mistake, I didn't add whole data structure (just three dots), there are array of objects like in the example on the stackblitz.

random · Accepted Answer · 2019-07-16 12:03:15Z

3

return is missing in Object.keys. As well instead of Object.keys use Object.entries to get key and value.

const objs = [{
  "B": {
    "value": 1,
  },
  "D": {
    "value": "45"
  },
  "E": {
    "value": "234"
  },
  "A": {
    "value": "543"
  },
  "C": {
    "value": "250"
  }
}];
const mapped = objs.map((key, _) => {
  return Object.entries((key)).map(([name, {
    value
  }]) => ({
    name,
    value
  }))
}).flat();

console.log(mapped);

edited Jul 16, 2019 at 12:03

answered Jul 16, 2019 at 11:57

random

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