javascript

Chapter 6: Object-Oriented Programming
Alternate Prototype Syntax
You may have noticed in the previous example that Person.prototype had to be typed out for each
property and method. To limit this redundancy and to better visually encapsulate functionality on the
prototype, it has become more common to simply overwrite the prototype with an object literal that
contains all of the properties and methods, as in this example:
function Person(){
}
Person.prototype = {
name : “Nicholas”,
age : 29,
job : “Software Engineer”,
sayName : function () {
alert(this.name);
}
};
In this rewritten example, the Person.prototype property is set equal to a new object created with an
object literal. The end result is the same, with one exception: the constructor property no longer points
to Person . When a function is created, its prototype object is created and the constructor is
automatically assigned. Essentially, this syntax overwrites the default prototype object completely,
meaning that the constructor property is equal to that of a completely new object (the Object
constructor) instead of the function itself. Although the instanceof operator still works reliably, you
cannot rely on the constructor to indicate the type of object, as this example shows:
var person = new Person();
alert(person instanceof Object); //true
alert(person instanceof Person); //true
alert(person.constructor == Person); //false
alert(person.constructor == Object); //true
Here, instanceof still returns true for both Object and Person, but the constructor property is
now equal to Object instead of Person . If the constructor ’ s value is important, you can set it
specifically back to the appropriate value as shown here:
function Person(){
}
Person.prototype = {
constructor: Person,
name : “Nicholas”,
age : 29,
job : “Software Engineer”,
sayName : function () {
alert(this.name);
}
};
This code specifically includes a constructor property and sets it equal to Person , ensuring that the
property contains the appropriate value.
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