creating an multidimensional Object dynamically from an multidimensional array

Question

Im trying to create an multidimensional Object like this one:

{ A : {a1: {},a2:{}}, B: {b1:{},b2:{}}}

from an multidimensional array like this one:

let array1 = [
      ['A', 'a1'],
      ['A', 'a1'],
      ['A', 'a2'],
      ['B', 'b1'],
      ['B', 'b1'],
      ['B', 'b2'],
    ];

I'm trying this for some hours now and was also reading plenty of entrys here on stackoverflow, but nothing really fits this specific case.

What i did so far:

    let array1 = [
      ['A', 'a1'],
      ['A', 'a1'],
      ['A', 'a2'],
      ['B', 'b1'],
      ['B', 'b1'],
      ['B', 'b2'],
    ];

    let object1 = {};

    array1.forEach(function (subArray) {
      let level1 = subArray[0];
      let level2 = subArray[1];

      object1[[level1]] = { ...{ [level2]: {} } };
    });

    console.log('object: ', object1);
    //desired output:  object = { A : {a1: {},a2:{}}, B: {b1:{},b2:{}}}
    //what I get:  object = { A : {a2:{}}, B: {b2:{}}}

So somehow in my code the entrys like {a1: {}} are getting overwritten in each iteration instead of adding a new entry.

Thanks a lot in advance.

Answer 1

Keep previous properties using ...object1[[level1]]:

    let array1 = [
      ['A', 'a1'],
      ['A', 'a1'],
      ['A', 'a2'],
      ['B', 'b1'],
      ['B', 'b1'],
      ['B', 'b2'],
    ];

    let object1 = {};

    array1.forEach(function (subArray) {
      let level1 = subArray[0];
      let level2 = subArray[1];

      object1[[level1]] = {
        ...object1[[level1]], // Keep previous properties
        ...{ [level2]: {} } // Add new
      };
    });

    console.log('object: ', object1);