Let's say I have the following code;
var A = {a:10};
var B = {b:20};
B.prototype = A;
alert(B.a);
I am getting undefined for B.a . Am I doing something wrong? How do I set the prototype for object literal ?
I know how to do for Constructor object. So the following code works perfect
function A(){this.a=10}
function B(){this.b=20}
B.prototype = new A();
b = new B;
alert(b.a);
How do I do it for object literal ?
Objects inherit from their constructor's prototype property, not their own. The constructor's prototype is assigned to the internal [[Prototype]] property that is available in some browsers as the __proto__ property.
So for b to inherit from a, you need to put a on b's inheritance chain, e.g.
Classic prototype inheritance:
var a = {a: 'a'};
function B(){}
B.prototype = a;
var b = new B();
alert(b.a); // a
Using ES5 Object.create:
var a = {a: 'a'};
var b = Object.create(a);
alert(b.a); // a
Using Mozilla __proto__:
var a = {a: 'a'};
var b = {};
b.__proto__ = a;
alert(b.a); // a
a, once a is on b's inheritance/prototype chain?
a's properties need to be augmented directly, e.g. a.foo = 'foo'. Assigning to b will create a property of b, even if a same–named property exists on a.
b will create a property on b" instead of "property of b".The prototype property is usually present in a Function object. This prototype should be an object, and this object is used to define the properties of an object created with a constructor.
// Plain object, no prototype property here.
var plainObject = {one: 1, two: 2};
// Constructor, a prototype property will be created by default
var someConstruct = function() {
// Constructor property
someConstruct.constructProp = "Some value";
// Constructor's prototype method
someConstruct.prototype.hello = function() {
return "Hello world!";
}
};
// Another constructor's prototype method
someConstruct.prototype.usefulMethod = function() {
return "Useful string";
}
var someInstance = new someConstruct();
console.log(someInstance.hello()); // => Hello world!
console.log(someInstance.usefulMethod()); // => Useful string
console.log(someConstruct.constructProp); // => Some value
console.log(someConstruct.prototype); // => {usefulMethod: function, hello: function}
console.log(plainObject.prototype); // => undefined
So, plain objects have no prototypes. Functions which work as constructors do have prototypes. These prototypes are used to fill an instance created with each construct.
Hope that helps :)
Only when using Function object that prototype is used, e.g. when you use a constructor. But no need of that for object literals.
Both of them are very good techniques, so it depends on what you want to do in a project and the JavaScript pattern you are using or like.
