How do I combine two objects by merging the values of same properties?

Is there a way we can combine two objects by nesting the values if properties are same instead of overwriting ?
Eg:

const obj1 = {a:10,b:13}
const obj2 = {a:84,c:70}

desired result : 
combinedObject = {a:{0:10,1:84}, b:13, c:70}