How do I use an array of indices to alter a specific item in a multi-dimensional object of unknown depth?

Question

Imagine I have an array, which looks like:

const x = ["a", "b", "c", "d"]

I wish to use it in order to navigate an object that I don't know the structure of, like:

const y = {
    "a": {
        "b": {
            "c": {
                "d": "Value I require"
            }
        },
        "f": ["g", "h"]
    },
    "e": null
}

However, my issue is that I don't know how deep y will be, or how many indices are in the array x. How do I do the following:

let someVariable = {"prefilled": "data"}
someVariable[x[0]][x[1]][x[2]][x[3]] = y[x[0]][x[1]][x[2]][x[3]]

In a way which is neither specific to the length of x, the depth of y (and also preferably isn't my current solution, which is a case statement upto a depth of 6)? For this simplified case, someVariable should hopefully look as follows:

{
    "prefilled": "data",
    "a": {
        "b": {
            "c": {
                "d": "Value I require"
            }
        }
    }
}

Also a duplicate of [Accessing nested JavaScript objects with string key](http://stackoverflow.com/q/6491463/218196) — Felix Kling, Jan 02 '17 at 18:44
@FelixKling Damnit, sorry about the duplicate. I guess I just couldn't phrase the question in the right way for Google ;). — Alexander Craggs, Jan 02 '17 at 18:47
No worries, searching can be difficult :) I guess that's an even better one: [How to set object property (of object property of..) given its string name in JavaScript?](http://stackoverflow.com/q/13719593/218196) — Felix Kling, Jan 02 '17 at 18:48

score 1 · Accepted Answer · answered Jan 02 '17 at 18:15

1

I would either use a tool like Lodash's _.get or implement something similar that can navigate an object:

let _ = require('lodash');
const x = ["a", "b", "c", "d"]
_.get(object, x.join('.'))

answered Jan 02 '17 at 18:15

Nick Tomlin

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A great answer! Especially considering I actually get my data in the format of "a.b.c.d" and turned it into an array for convenience. Allows me to also do `_.set` to set the other object instance, as a note to future readers. – Alexander Craggs Jan 02 '17 at 18:25

score 1 · Answer 2 · answered Jan 02 '17 at 18:19

You could iterate the array and walk the object.

const getValue = (object, path) => path.reduce((o, k) => (o || {})[k], object),
      y = { a: { b: { c: { d: "Value I require" } }, f: ["g", "h"] }, e: null },
      x = ["a", "b", "c", "d"]

console.log(getValue(y, x));

How do I use an array of indices to alter a specific item in a multi-dimensional object of unknown depth?

2 Answers2