Why not use prototype for Song.isPlaying?

Hi Raphael, thanks for the answer. I'm still a bit confused because, I had wrote my code with the isPlaying as a prototype and it still works. From my understanding with MDN the new already creates the property for the Song Object every time we assign a new instance to a variable and I'm able to access it and change it locally to individual vars new Song was made under.

MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

//Console Tester
function Song(title, artist, duration) {
  this.title = title;
  this.artist = artist;
  this.duration = duration;
}
Song.prototype.isPlaying = false;

var songOne = new Song()
var songTwo = new Song()

console.log(songOne.isPlaying) //returns false
console.log(songTwo.isPlaying) //returns false

//Local Changes to songOne
songOne.isPlaying = true;

console.log(songOne.isPlaying) //returns true <--
console.log(songTwo.isPlaying) //returns false

I'm still trying to grasp prototypes but I believe we are excluding functions because we don't want the functions' large code to use up compiler time every time we create a new object so we just refer to it's name. Does using prototype for properties help with efficiency by not having to run through each of them each time we create a new object?

E.g. function Object() { this.property (x 500000000 times) = value; } -- vs -- Object.prototype.property (x 5000000 times) = value

Will var object = new Object save on having to execute the 5000000 lines of this.property if I create it through prototype? Are prototyping properties efficiently done through a prototype reference or are all prototype.property declarations also being run through the compiler? (Hope this make sense, otherwise I could seriously be confusing myself haha)

Great questions! I'm waiting for answers either! Thanks! =)