mongoose put vs push code example

Example 1: add items to a list in a document monoose

const {name , id} = req.body
    Category.update(
        {_id: id}, 
        {$push: {items: {"name": name}}},{new: true, upsert: true }).exec();
        res.sendStatus(200)

Example 2: how to append data to a field in mongoose model

exports.addFriend = function (req, res, next)
{
var friend = {"firstName": req.body.fName, "lastName": req.body.lName};
Users.findOneAndUpdate({name: req.user.name}, {$push: {friends: friend}});
};