Recursive String Parsing into Object in JavaScript

We are required to write a JavaScript function that takes in an array of strings and returns an object corresponding to the strings.

For example −

If the array is −

const arr = [
   "country.UK.level.1",
   "country.UK.level.2",
   "country.US.level.1",
   "country.UK.level.3"
];

Then the output should be −

const output = {
   "country": [
       {"UK" : {"level" : ["1", "2", "3"]}},
       {"US" : {"level" : ["1","2"]}}
  ]
}

Conditions

Strings stored in the str array will not be sorted and the code should be robust against that.

Strings will follow the x.y.x.y... pattern, where x will be unique for that array and y can change. In my example country and level will always be the same as they represent the x pos.

This requires recursive approach as the strings stored in the str array, can be of any length. The longer the string the deeper nesting.

Example

Following is the code −

const arr = [
   "country.UK.level.1",
   "country.UK.level.2",
   "country.US.level.1",
   "country.UK.level.3"
];
const stringToObject = arr => {
   const obj = {};
   arr.forEach(str => {
      let curr = obj;
      let splitted = str.split('.');
      let last = splitted.pop();
      let beforeLast = splitted.pop();
      splitted.forEach( sub => {
         if(!curr.hasOwnProperty(sub)){
            curr[sub] = {};
         };
         curr = curr[sub];
      });
      if(!curr[beforeLast]){
         curr[beforeLast] = [];
      };
      curr[beforeLast].push(last);
   });
   return obj;
};
console.log(JSON.stringify(stringToObject(arr), undefined, 4));

Output

This will produce the following output on console −

{
   "country": {
       "UK": {
           "level": [
               "1",
               "2",
               "3"
           ]
       },
       "US": {
           "level": [
               "1"
           ]
       }
   }
}