Prototipos de JavaScript

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Todos los objetos JavaScript heredan propiedades y métodos. a partir de un prototipo.

En el capítulo anterior aprendimos cómo usar un constructor de objetos:

Ejemplo

function Person(first, last, age, eyecolor) {
   
this.firstName = first;
  this.lastName = last;
   
this.age = age;
   
this.eyeColor = eyecolor;
}

const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");

Pruébelo usted mismo →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Objects</h2>

<p>Using an object constructor:</p>

<p id="demo"></p>

<script>
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}

const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");

document.getElementById("demo").innerHTML =
"My father is " + myFather.age + ". My mother is " + myMother.age; 
</script>

</body>
</html>

También aprendimos que no puedes agregar una nueva propiedad a un constructor de objetos existente:

Ejemplo

Person.nationality = "English";

Pruébelo usted mismo →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Objects</h2>

<p>You cannot add a new property to a constructor function.</p>

<p id="demo"></p>

<script>
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}

Person.nationality = "English";

const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");

document.getElementById("demo").innerHTML =
"The nationality of my father is " + myFather.nationality; 
</script>

</body>
</html>

Para agregar una nueva propiedad a un constructor, debe agregarla al función constructora:

Ejemplo

function Person(first, last, age, eyecolor) {
   
this.firstName = first;
   
this.lastName = last;
   
this.age = age;
   
this.eyeColor = eyecolor;
  this.nationality = "English";
}

Pruébelo usted mismo →

<!DOCTYPE html>
<html>
<body>

<h1>JavaScript Objects</h1>

<p>Using an object constructor:</p>

<p id="demo"></p>

<script>
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
  this.nationality = "English";
}

const myFather = new Person("John", "Doe", 50, "blue");
const myMother = new Person("Sally", "Rally", 48, "green");

document.getElementById("demo").innerHTML =
"The nationality of my father is " + myFather.nationality + ". The nationality of my mother is " + myMother.nationality;
</script>

</body>
</html>

Herencia de prototipo

Todos los objetos JavaScript heredan propiedades y métodos de un prototipo:

Los objetos Fecha heredan de Fecha.prototype
Los objetos Array heredan de Array.prototype
Los objetos Persona heredan de Person.prototype

El Object.prototype está en la parte superior de la cadena de herencia del prototipo:

Objetos Fecha, objetos Matriz y Persona los objetos heredan de Object.prototype.

Agregar propiedades y métodos a objetos

A veces desea agregar nuevas propiedades (o métodos) a todos los objetos existentes de un tipo determinado.

A veces desea agregar nuevas propiedades (o métodos) a un objeto. constructor.

Usando la propiedad prototype

La propiedad prototype de JavaScript le permite agregar nuevas propiedades al objeto. constructores:

Ejemplo

function Person(first, last, age, eyecolor) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eyecolor;
}

 Person.prototype.nationality = "English";

Pruébelo usted mismo →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Objects</h2>

<p>The prototype property allows you to add new methods to objects constructors:</p>

<p id="demo"></p>

<script>
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}

Person.prototype.nationality = "English";

const myFather = new Person("John", "Doe", 50, "blue");
document.getElementById("demo").innerHTML =
"The nationality of my father is " + myFather.nationality; 
</script>

</body>
</html>

La propiedad prototype de JavaScript también le permite agregar nuevos métodos a los objetos. constructores:

Ejemplo

function Person(first, last, age, eyecolor) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
  this.eyeColor = eyecolor;
}

 Person.prototype.name = function() {
    return this.firstName + " " + this.lastName;
};

Pruébelo usted mismo →

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Objects</h2>

<p id="demo"></p>

<script>
function Person(first, last, age, eye) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eye;
}

Person.prototype.name = function() {
  return this.firstName + " " + this.lastName
};

const myFather = new Person("John", "Doe", 50, "blue");
document.getElementById("demo").innerHTML =
"My father is " + myFather.name(); 
</script>

</body>
</html>

Modifique únicamente sus propios prototipos. Nunca modifique los prototipos de objetos JavaScript estándar.