Create an object with selected value and optiongroup label

Question

Let's suppose I have this dropdown with multiselection:

<select id='grp_option'>
  <optgroup label="Group 1">
    <option value='Option 1.1'>Option 1.1</option>
  </optgroup> 
  <optgroup label="Group 2">
    <option value='Option 2.1'>Option 2.1</option>
    <option value='Option 2.2'>Option 2.2</option>
  </optgroup>
</select>

I would like to create an array of object like this:

let array = [];
let obj, obj2;
obj[label] = value;
obj2[label2] = value2;
array.push(obj);
array.push(obj2);

Where label is the optgroup label of each selected option and value is the value of each selected option.

Do you have any idea? Thank you