Create Dynamically Nested Objects with loops

Question

I wanna create a nested object dynamically. I can create it hard coded. Is it possible to do this with a loop ?

result = {}
keys = ["a", "b", "c", "d"]

result[keys[0]] = {}
result[keys[0]][keys[1]] = {}
result[keys[0]][keys[1]][keys[2]] = {}
result[keys[0]][keys[1]][keys[2]][keys[3]] = "cool"

I want to pass an integer for example if it is "3", this should created an object like:

result = {
  "a": {
     "b": {
        "c": "cool"
     }
   }
}

If it is 4, :

result = {
  "a": {
     "b": {
        "c": {
           "d": "cool"
        }
     }
   }
}

So on ...

edit:

I am also checking result object, in order to create this nested structure. If there is not any field yet, I simply create the object.

Using this structure to group data. Any chance to check these dynamically ?

if (!result[keys[0]]) 
if (!result[keys[0]][keys[1]]) 
if (!result[keys[0]][keys[1]][keys[2]])

will keys contain the correct number of input (what if the input is 5)? — depperm
– depperm, Commented Jul 10, 2019 at 15:59
You could do it using recursion and map the index of the iteration with its alphabetical representation. — Jordan Enev
– Jordan Enev, Commented Jul 10, 2019 at 16:01
@depperm Getting keys as a param of this function. It might change in the future. This is why ı am looking for dynamic solution. You can basically use keys.length in order to determine. — Caner Sezgin
– Caner Sezgin, Commented Jul 10, 2019 at 16:01
what problem you have? do you asking how to use for-loop in javascript? — apple apple
– apple apple, Commented Jul 10, 2019 at 16:02

Mark · Accepted Answer · 2019-07-10 16:13:32Z

6

You can use reduceRight() for this. It just starts from the inside at the last item in the keys list and works its way out starting with "cool":

let keys = ["a", "b", "c", "d"]
let limit = 3

let result = keys.reduceRight((obj, key) => ({[key]: obj}), "cool")

console.log(result)

To limit where the object stops you can iterate over a slice of the keys. For example:

let keys = ["a", "b", "c", "d"]
let start = 0
let stop = 3 // slices are don't inlcude the last item, so this will stop at index 2

let result = keys.slice(start, stop).reduceRight((obj, key) => ({
  [key]: obj
}), "cool")

console.log(result)

edited Jul 10, 2019 at 16:13

answered Jul 10, 2019 at 16:04

Mark

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7 Comments

Keith Over a year ago

OP say's he wants to pass an integer, so maybe your keys could be -> Array(3).fill().map((f, ix) => String.fromCharCode(97 + ix)).reduceRight(.... etc

Karl-André Gagnon Over a year ago

There's a reduceRight function?! Oh well, time to do some refactoring. "I want to pass an integer for example if it is "3", this should created an object like [object three levels deep]." Might need to add a slice before the reduce

Caner Sezgin Over a year ago

Perfect ! Any chance to use that between in range. Like start with index 1 ("b") and ends with index 2 ("c")

Mark Over a year ago

Thanks @Keith, I missed that part.

Caner Sezgin Over a year ago

@MarkMeyer Amazing, you’re a great help ! Thank you so much.

|

Nina Scholz · Accepted Answer · 2019-07-10 16:47:36Z

1

If you like to add to a given object a new property, you could reduce the keys with the object and take default objects for not given keys. At the end assign the value.

function setValue(object, path, value, limit) {
    var keys = path.slice(0, limit),
        last = keys.pop();

    keys.reduce((o, k) => o[k] = o[k] || {}, object)[last] = value;
    return object;
}

var result = { foo: 42 },
    keys = ["a", "b", "c", "d"];

setValue(result, keys, 'cool');
console.log(result);

setValue(result, keys, 'cool', 3);
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Jul 10, 2019 at 16:47

Nina Scholz

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Comments

CrackerKSR · Accepted Answer · 2022-11-16 09:27:25Z

1

short and simple using reduce

let object1= {}
keys = ['a', 'b', 'c']

keys.reduce((prev,curr,i)=>{
    prev[curr] = {}
    return prev[curr]
}, object1)

log(object1) 
// {
//   a:{
//     b:{
//        c:{}
//     }
//   }
// }

answered Nov 16, 2022 at 9:27

CrackerKSR

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Comments

apple apple · Accepted Answer · 2019-07-10 16:13:34Z

0

simple for-loop solution.

let result = {}
let keys = ["a", "b", "c", "d"]
let depth=3;

let current = result
for(let i=0;i<depth;++i){
  let key = keys[i]
  if(i == depth-1) current[key] = 'cool'
  else current = current[key] = {}

}

console.log(result)

answered Jul 10, 2019 at 16:13

apple apple

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Comments

Brian Swisher · Accepted Answer · 2019-07-12 14:39:34Z

-1

I'd use a reducer, along with some basic tests to help me out: https://youtu.be/D6zLI8zrfVs

https://gist.github.com/brianswisher/2ce1ffe3ec08634f78aacd1b7baa31f9

edited Jul 12, 2019 at 14:39

answered Jul 10, 2019 at 23:30

Brian Swisher

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