Setting n-th subobject based on array of keys

April 16, 2023

I have object pivot, that has multiple accessors of different depths.

For keys array const keys = ['rotation'] I want my code to assign value x like this:

pivot['rotation'] = x

And for array const keys = ['rotation', 'y'] I want the code to do this:

pivot['rotation']['y'] = x

Solution I tried looks like this:

accessors.forEach(a => accessor = accessor[a])
accessor = x

However, after logging the accessor value, I found out it’s just primitive value of 0.1, instead of an object reference.

Can I get the object reference somehow? Or do I need to go a different path to achieve this?

Working code would also be something ugly like next example, which is not acceptable.

if (accessors.length == 1) {
    pivot[accessors[0]] = x
} else if (accessors.length == 2) {
    pivot[accessors[0]][accessors[1]] = x
}

>Solution :

here is something similar to lodash set. keep in mind this mutates the object

const pivot = {}

const set = (obj, path, value) => {
  // Regex explained: https://regexr.com/58j0k
  const pathArray = Array.isArray(path) ? path : path.match(/([^[.\]])+/g)
  const pathLength = pathArray.length;
  pathArray.reduce((acc, key, i) => {
    if (acc[key] === undefined) acc[key] = {}
    if (i === pathLength - 1) acc[key] = value
    return acc[key]
  }, obj)
}
set(pivot, ['rotation', 'x'], 'y');

console.log(pivot);

since your path is already an array you don’t need the regex part

const pivot = {}
const set = (obj, path, value) => {
  const pathLength = path.length;
  path.reduce((acc, key, i) => {
    if (acc[key] === undefined) acc[key] = {}
    if (i === pathLength - 1) acc[key] = value
    return acc[key]
  }, obj)
}

set(pivot, ['rotation', 'x'], 'y');

console.log(pivot);