Javascript - (Prototype Model|Prototypical object)

About

A prototype-based language has the notion of a prototypical object.

A prototypical object is used as a template from which to get the initial properties for a new object.

Any object can:

  • specify its own properties, either when you create it or at run time.
  • be associated as the prototype for another object, allowing the second object to share the first object's properties.

Since ECMAScript 2015, a class can be used in place of prototyping for object creation and inheritance

Management

Chain

The father of all prototype is: Object.prototype. See Javascript - Prototype Chain - Hierarchy (Sort of Inheritance)

Get

To get the prototype of an object check the __proto__ attribute.

var element = document.querySelector("body");
console.log(element.__proto__.toString())

Example

Object.create

Basic

var foo = { a: 42 }; 

// create `bar` and link it to foo 
var bar = Object.create( foo ); 

bar.b = "hello world from bar.b"; 
console.log( bar.b ); // "hello world" 
console.log ("The property 'bar.a' was delegated to the foo prototype. 'bar.a'  has the value "+  bar.a ); // 42 <-- delegated to ` foo `

foo.hello = "hello from foo";
console.log ("Attributes added after the initialization are also seen.")
console.log(" The new property 'foo.hello' can be accessed by 'bar': "+bar.hello ); 

Library with prototype

Constructor and prototype

A prototype can be added to a constructor.

// An object
var person = {
   name: "Nicolas", 
   length: 180
};
 
// A constructor
function ColoredPerson() {
    // Rode piet !
    this.color = "red";
}
 
// Set the prototype to be the person object (dynamic inheritance)
ColoredPerson.prototype = person;
 
// Create a new object
var coloredPerson = new ColoredPerson();

console.log ( "The object:")
console.log (coloredPerson);

console.log ( "The object prototype:")
console.log (coloredPerson.__proto__);

console.log ( "The object prototype can be directly accessed. Example with the name:")
console.log (coloredPerson.name);

Management

Source of a property (prototype or object)

Prototype inheritance works with a constructor (Always ??)

// An object
var person = {
   name: "Nicolas", 
   length: 180
};

// A constructor
function ColoredPerson() {
    // Rode piet !
    this.color = "red";
}

// Set the prototype to be the person object (dynamic inheritance)
// All new ColoredPerson must inherit its properties.
ColoredPerson.prototype = person;

// Create a new object
var coloredPerson = new ColoredPerson();

// Loop through the properties
var propSource;
for (var prop in coloredPerson) {
    if (coloredPerson.hasOwnProperty(prop)) {
        propSource = "object";
    } else {
        propSource = "prototype";
    }
    console.log("The property " + prop + " (value:" + coloredPerson[prop] + ") is a property from the " + propSource);
}

Prototype Hierarchy

A function that prints the prototype of the prototype of the .. See Javascript - Prototype Chain - Hierarchy (Sort of Inheritance)

Documentation / Reference


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