oloo.js

const Cow = {
  airInLungs: 0,
  getAirInLungs() {
    return this.airInLungs
  },
  breathe () {
    this.airInLungs = this.lungCapacity
  },
  moo () {
    let output = "m"
    let air = this.getAirInLungs()
    while (air --> 0) { // The 'goes to' operator
      output += "o"
    }
    this.airInLungs = air
    return output
  }
}
const CowFactory = lungCapacity => ({
  __proto__: Cow,
  lungCapacity
});
const herd = []
for (let i = 0; i < 30000; i++) {
  const cow = CowFactory(i);
  cow.index = i
  herd.push(cow)
}
console.log(process.memoryUsage())
const start = Date.now()
herd.map(cow => {
  cow.breathe()
  cow.moo()
})
console.log(`Finished mooing in ${(Date.now() - start) / 1000} seconds`)

/*
My results…
➜ class-vs-closures node classes.js
{ rss: 25632768, heapTotal: 11571200, heapUsed: 6076680 }
Finished mooing in 8.192 seconds
➜ class-vs-closures node closures.js
{ rss: 38068224, heapTotal: 29396992, heapUsed: 15660968 }
Finished mooing in 14.56 seconds
➜ class-vs-closures node oloo.js
{ rss: 27602944, heapTotal: 16814080, heapUsed: 6630416 }
Finished mooing in 8.212 seconds
*/