How to copy source object keys to target object keys in javascript

Question

I am facing a situation where I need to copy source object to target object. My source and target objects are nested object.

source object :

let remoteOptionObject = {
                    "key1" : "1",
                    "key2" : "2",
                    "key3" :{
                        "key5" : "5"
                    }
               }

target object:

let localOptionObject = {
                    "Key1" : "1",
                    "Key2" : "2",
                    "Key3" :{
                        "Key4": "4",
                        "key5" : "5"
                    }, 
                    "key6" : "6",
                }

expected result :

let expectedLocalObj= {
                    "Key1" : "1",
                    "Key2" : "2",
                    "Key3" :{
                        "Key4": "4",
                        "key5" : "5"
                    }, 
                    "key6" : "6",
                }

Here I want to retain the keys of target and update only those which are present in source Object. I have tried with Object.assign({}, target, source} but that is removing keys which are nested (as expected).

Below is what I have tried and its working but is this a correct approach.

function assignSourceToTarget(source, target){
    for (var property in source) {
        if(typeof source[property] === 'object') {
            if (!target[property]) Object.assign(target, { [property]: {} });
            assignSourceToTarget(source[property], target[property]) 
        } else {
            if(source.hasOwnProperty(property)) {
                target[property] = source[property]
            }
        }        
    }
    return target;
}