explain how prototype works

prototype.js

function test() {}
test.prototype.number = 5;

var a = new test
var b = new test

b.number // 5

b.hasOwnProperty("number") // false <- false because number is on the prototype
b.number = 10 // now were assigning to number, putting it on the instance
a.number // 5 <- hasn't changed, we haven't modified the prototype

b.hasOwnProperty("number") // true <- now this is true becasue its on the instance
delete b.number

b.hasOwnProperty("number") // false
b.number // 5 <- five again, because it finds "number" on the prototype