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JavaScript Object-Oriented JavaScript (2015) Constructor Functions and Prototypes Methods with Prototypes

Is my assumption about prototypes correct?

My definition: prototypes are essentially creating methods on a constructor function but from outside the constructor function.

Is my definition correct?

Let's say we have a constructor function that creates a new user:

function User(first_name, last_name, email, password, friends, favorites) {
    this.first_name = first_name;
    this.last_name = last_name;
    this.email = email;
    this.password = password;
    this.friends = [];
    this.favorites = [];

I want to create a few methods that allow the user to add/delete friends and add/delete favorites:

User.prototype.add_friend = function(friend) {
    this.friends = this.friends.push(friend);

User.prototype.delete_friend = function(friend) {
    //this.favorites = this.friends.indexOf(friends).delete;

User.prototype.add_favorite = function(favorite) {
    this.favorites = this.favorites.push(favorite);

User.prototype.delete_favorite = function(favorite) {
    //this.favorites = this.favorites.indexOf(favorite).delete;

By the way, I am not sure how to delete an array item at a given index... so if you could help me out there that would be great!!! Thanks guys!

1 Answer

Steven Parker
Steven Parker
215,958 Points

The main difference is that a function defined in the constructor will be replicated for each instance of the object. A prototype function will be shared by the instances. If you were going to have a large number of objects the memory usage could become significant.

:point_right: You can remove one or more array item(s) using splice(index, count).


var dogs = ["Beagle", "Pointer", "Mutt", "Weiner", "Labrador"];
dogs.splice(2, 2);
// dogs will now be ["Beagle", "Pointer", "Labrador"];

Splice will also insert items into the array. Look it up from a good reference like MDN.