looping through objects within an object with Object.assign

The script below currently outputs:

{
    "title1": {
        "0": "undefined"
    },
    "title2": "& three",
    "title3": "& four"
}

My question is what is required in the if statement to successfully loop through the properties of the [key][innerKey] and pass them through the encode function and return them to 'out'?

I have been trying to solve it using a for loop within the first part of the if statement without success. I figure it needs to follow a logic along the lines of:

• if arr[key] is an object then
• output the [key]:
• then loop through all properties of the [key]
• and pass them through the function encode
• and return them to 'out'

thanks.

var arr = {
  "title1": {
    "nested1": "one",
    "nested2": "& two"
  },
  "title2": "& three ",
  "title3": "& four"
};

var encodedValues = Object.keys(arr).reduce(function(out,key,innerKey) {

  if (typeof arr[key] == "object") {
     return Object.assign(out, {[key]: {[innerKey]: encode(arr[key][innerKey])}})

  } else {
     return Object.assign(out, {[key]: encode(arr[key])})
  }

}, {});

console.log(encodedValues)