This npm module extends mongoose schema (returning new one)
NOT mongoose-schema-extend but mongoose-extend-schema
$ npm i --save mongoose-extend-schemaconst extendSchema = require('mongoose-extend-schema');
const UserSchema = new mongoose.Schema({
  firstname: {type: String},
  lastname: {type: String}
});
const ClientSchema = extendSchema(UserSchema, {
  phone: {type: String, required: true}
});const mongoose = require('mongoose');
const extendSchema = require('mongoose-extend-schema');
const UserSchema = new mongoose.Schema({
  email: {type: String, unique: true, required: true},
  passwordHash: {type: String, required: true},
  firstname: {type: String},
  lastname: {type: String},
  phone: {type: String}
});
// Extend UserSchema
const AdminUserSchema = extendSchema(UserSchema, {
  firstname: {type: String, required: true},
  lastname: {type: String, required: true},
  phone: {type: String, required: true}
});
const User = mongoose.model('users', UserSchema);
const AdminUser = mongoose.model('admins', AdminUserSchema);
const john = new User({
  email: 'user@site.com',
  passwordHash: 'bla-bla-bla',
  firstname: 'John'
});
john.save();
const admin = new AdminUser({
  email: 'admin@site.com',
  passwordHash: 'bla-bla-bla',
  firstname: 'Henry',
  lastname: 'Hardcore',
  // phone: '+555-5555-55'
});
admin.save();
// Oops! Error 'phone' is requiredconst mongoose = require('mongoose');
function extendSchema (Schema, definition, options) {
  return new mongoose.Schema(
    Object.assign({}, Schema.obj, definition),
    options
  );
}
module.exports = extendSchema;@doasync