extendy.js

// extendy is a higher-order frunction that wraps to constructors 
// and allows b to "inherit" from a
extendy = (a) => ( b) => (opts={}) => Object.assign({}, a(opts.super || {}), b(opts))
​
// create a cow "constructor"
cow = (opts={}) => ({utters: opts.utters || 4, milk: () => "got milk?"})
​
// create a stawbery cow "constructor" that extends cow
strawbery = extendy(cow)((opts={}) => ({flavor: 'strawbery', expires: opts.expires || 'tomorrow'}))
​
// with all defaults
strawbery() 
​
// overwrite strawbery prop
strawbery({expires: 'lulwat'}) // override strawbery prop
​
// opverwrite super prop
pinkcow = strawbery({expires: 'lulwat', super: {utters: 8}}) // override super prop :p
​
// pinkcow is an "strawbery" but has "cow"'s method 'milk'
pinkcow.milk()