Prototype

• Adding a function as a property would lead to each instance having a copy of all functions.
• Instead, there is a prototype for each constructor which contains all the properties every instance gets.

function Rectangle(w, h){
        this.width = w;
        this.height = h;
}

Rectangle.prototype.area = function() {
        return this.width * this.height;
}
        
var r1 = new Rectangle(2,3);

r1.area()

• Thus, an object inherits properties from its prototype object.
• Use hasOwnProperty("area") to determine if "area" is not inherited.
• A prototype object can inherit from its own prototype object, and so on.......
• The properties' values are not copied at creation time. They are dynamically looked up at runtime.
• Look up happens only when reading the value of a property. When writing, the object obtains its own copy of the property, if inherited.