this pattern has usually been used in Java for testing. but, in javascript, it's very easy to do without the boilerplate code hassle.

builder pattern in javascript.js

// general helper to create the builder pattern automatically
var make = function(klass) { 
  return { with: function(extendWithThis) { return Object.assign(klass, extendWithThis) } }
}

// let's make a spaghetti
var Pasta = { ingredients: [] }

var spaghetti = make(Pasta).with({
  ingredients: [ 'mashroom', 'onion' ]
})

// let's make another spaghetti with blognose sauce
var spaghettiBolognese = make(spaghetti).with({
  sauce: [ 'bolognese' ]
})