How to pad an array in an object without overwriting the object?

Question

Node.js

How to write to range object without overwriting array in object [dataOperator.b]

range = { [dataOperator.a]: { [dataOperator.b]:  await output( dataOperator ) } }

// Должно получиться как-то так
range ={ '1':{ '2':[ 32,33,34 ] };
range ={ '1':{ '2':[ 32,33,34,78,75,31 ] };