Modifying a string value via a callback in JavaScript

var object = {
  item: {
    content: ""
  },
  collection: []
}

function preprocess(callback) {
// ...
}

preprocess(({ collection, content }) => {
    content = "new content"
    collection = ["new-item-1", "new-item-2", "new-item3"];
});

console.log(object.item.content)
// => "new content"

function preprocess(callback) {
  callback({collection: object.collection, content: object.item.content})
}