Setting the value of a multidimensional object or array property in Javascript

Question

Yes I know how to loop through arrays (types) in Javascript. The fact is, I'd like to know how to set a multiDimensionalArray array's value by a set of given indexes to keep it as generic as possible. For example I've an array with a length of 3 (which could as well be a length of 4, 100, ...):

var indexes = [0, "title", "value"];

I know the multidimensional array (mArray) can be set by putting the indexes like so:

multiDimensionalArray[0]["title"]["value"] = "Jeroen"; or multiDimensionalArray[indexes[0]][indexes[1]][indexes[2]] = "Jeroen";

The fact that the given indexes array can vary and does not always contain the same index names so I'm search for a solution like this:

multiDimensionalArray[indexes] = "Jeroen";

I don't know how to code the assignation if this. I've searched on Google/Stack Overflow. Maybe I'm using the wrong keywords. Can anyone help me?

Thanks!

Jeroen Boumans · Accepted Answer · 2017-07-12 09:02:28Z

1

Following example is how I've made it working thanks to Jonas's example:

var json = [{
  "hello": {
    "world": 1,
    "world2": 2
  },
  "bye": {
    "world": 1,
    "world2": 2
  }
}];

var indexes = [0, "hello", "world2"];
var value = "value";

indexes.slice(0,-1).reduce((obj, index) => obj[index], json)[indexes.pop()] = value;
console.log(json);

answered Jul 12, 2017 at 9:02

Jeroen Boumans

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Jonas Wilms · Accepted Answer · 2017-07-12 09:12:24Z

0

So imagine you have a structure like this:

var array=[[["before"]]];

Then you want

var indexes=[0,0,0];
var value="value";

to actually do:

array[0][0][0]="value";

which can be easily achieved with reduce:

indexes.slice(0,-1).reduce((obj,index)=>obj[index],array)[indexes.pop()]=value;

Explanation:

indexes.slice(0,-1) //take all except the last keys and
.reduce((obj,index)=>obj[index] //reduce them to the resulting inner object e.g. [0,0] => ["before"]
,array) //start the reduction with our main array
[indexes.pop()]=value;// set the reduced array key to the value

    var array=[[[0]]];


    var indexes=[0,0,0];
    var value="value";
    indexes.slice(0,-1).reduce((obj,index)=>obj[index],array)[indexes.pop()]=value;
    
    console.log(array);

edited Jul 12, 2017 at 9:12

answered Jul 11, 2017 at 14:51

Jonas Wilms

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3 Comments

Jeroen Boumans Over a year ago

How could this work when using textual indexes like mentioned in the question? I cannot seem to get it working when replacing the zeroes in you example by textual indexes. I'm using textual indexes since the multiDimensionalArray can also contain object data.

Jeroen Boumans Over a year ago

It worked by replacing indexes.slice(-1) with indexes.slice(0, -1)

Jonas Wilms Over a year ago

@jeroen oh right, thanks for the info. Im sorry for that obvious mistake... :/

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