原型继承和静态方法

Question

I'm trying to get used to the "real" prototypal inheritance of JavaScript (ECMAScript 5) but somehow my mind seems to be stuck in the classical inheritance pattern.

I'd like to create a Vector object which performs simple operations such as adding, subtracting etc.

Now there are two scenarios:

• #1: Adding Vector B "to" Vector A (Vector A gets modified)
• #2: Adding Vector B "to" Vector B (a new Vector C is created, which is the sum of A and B)

In classical inheritance I'd create an instance method for scenario #1 and a static method for case #2 but it seems like there are no static functions in prototypal inheritance.

So, what's a clean way to realize these two scenarios?

Here's what I've got so far:

var Vector = {

  x: 0,
  y: 0,
  z: 0,

  initialize: function(x,y,z) {
    this.x = x;
    this.y = y;
    this.z = z;
    return this;
  },

  add: function(vec) {
    this.x += vec.x;
    this.y += vec.y;
    this.z += vec.z;
    return this;  
  },

  print: function() {
    console.log('x:', this.x, 'y:', this.y, 'z:', this.z);
  }
};

var firstVector = Object.create(Vector).initialize(1,2,3);
var secondVector =  Object.create(Vector).initialize(4,5,6);

firstVector.print();  // Outputs: x:1, y:2, z:3
secondVector.print(); // Outputs: x:4, y:5, z:6

firstVector.add(secondVector); 
firstVector.print(); // Outputs: x:5,y:7,z:9


// What I'm looking for:

var thirdVector = Vector.add(firstVector, secondVector);

Thanks for any advice!

Update :

Here is my attempt to implement a static function using Paul's advice (thanks!):

var vectorPrototype = {
  hello: function() { console.log('hello I am the prototype'); }
};

var Vector = Object.create(vectorPrototype);

Vector.hello = function() { console.log('hello I am the static function'); };

Vector.init = function() {
  return Object.create(vectorPrototype);
}

var vec1 = Vector.init();

vec1.hello(); // says: 'hello I am the prototype'
Vector.hello(); // says: 'hello I am the static function'

Answer 1

Your Vector object is really just the prototype. You can use it with the Object.create function to create your Vector base/sub class. Then stick your static properties on your newly created Vector class. See here: http://jsfiddle.net/agYNc/1/

var vectorPrototype = {

  x: 0,
  y: 0,
  z: 0,

  initialize: function(x,y,z) {
    this.x = x;
    this.y = y;
    this.z = z;
    return this;
  },

  add: function(vec) {
    this.x += vec.x;
    this.y += vec.y;
    this.z += vec.z;
    return this;  
  },

  print: function() {
    console.log('x:', this.x, 'y:', this.y, 'z:', this.z);
  }
};

//create your base Vector type
var Vector = Object.create( vectorPrototype );


//Your static functions here
Vector.staticFunction = function ( vec1, vec2 ) {};


var firstVector = Object.create(Vector).initialize(1,2,3);
var secondVector =  Object.create(Vector).initialize(4,5,6);

firstVector.print();  // Outputs: x:1, y:2, z:3
secondVector.print(); // Outputs: x:4, y:5, z:6

firstVector.add(secondVector); 
firstVector.print(); // Outputs: x:5,y:7,z:9​

Here is a good example of using Object.create with inheritance, static and instance properties. https://github.com/webadvanced/takeCommand/blob/master/src/takeCommand.module.js