save array to mongodb and push code example

Example 1: mongodb push to arry in update

db.collection.update({_id:xx}, {$push:{letters : {$each:['first one'], $position:0}}})

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}});
};