Add field not in schema with mongoose

You can add and remove fields in schema using option { strict: false }

option: strict

The strict option, (enabled by default), ensures that values passed to our model constructor that were not specified in our schema do not get saved to the db.

var thingSchema = new Schema({..}, { strict: false });

And also you can do this in update query as well

Model.findOneAndUpdate(
  query,  //filter
  update, //data to update
  { //options
    returnNewDocument: true,
    new: true,
    strict: false
  }
)

You can check the documentations here

You can add new fields in schema User using .add

require('mongoose').model('User').schema.add({fullName: String});

Thanks.-