How to get arguments when while setting up the prototype manually?

Tell us what’s happening:
I understood fully how to add more properties and methods to an object and how we should set the constructor later, but I just wonder how we get arguments from the user into those new properties?

Your code so far

function Animal(name,legs){
  this.name=name;
  this.legs=legs;
}

//Animal.prototype ={
// constructor:Animal(name,legs,species),
//super(name,legs);
//this.species=species
//}

Animal.prototype ={
  constructor:Animal,
  species="birds"
}

const duck=new Animal("ducky",2);
console.log(duck.constructor);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36.

Link to the challenge:
I can’t include links yet but this is the lesson for more info
//https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/object-oriented-programming/change-the-prototype-to-a-new-object

Hello!

Well, I guess there would be a mechanic such as every time the user presses a certain button, it triggers a “new Animal” where the values come from inputs. You would get the inputs with something like that then store the values into variables and populate your new Animal(variables)