Exploring JS topics - Objects and Inheritance

objects.js

/* =========== JavaScript Objects =================== */

//Prototypes & Inheritance
//Creates a custom prototype object using inherit()
var book = {
    title: "",
    author: "",
    ISBN: null
};
var book1 = inherit(book);              //book is prototype for book1

book1.publishYear = 1994;               //adds a new property
book1.title = "This is my book";        //Change book1 title
book.title = "blank";                   //change prototype title
var book2 = inherit(book);              //creates new book object

//Prints book1 year & title
console.log("book1 = " + book1.publishYear + " " + book1.title);
//Prints prototype title
console.log("book = " + book.title);
//Prints book2 title which is inherited from prototype
console.log("book2 = " + book2.title);
//Property subtitle does not exist --> undefined
console.log("book2 subtitle = " +book2.subtitle);

//Delete a property
delete book1.publishYear
console.log("\nbook1 - removing property: " + book1.publishYear + " " + book1.title);

//Testing properties
console.log("book is enumerable? " + book.propertyIsEnumerable("title"));
console.log("book2 has own author property? " + book2.hasOwnProperty("author"));

//Iterate through properties
for(p in book){
    console.log("book property: " + p);
}

for(p2 in book1){
    console.log("book1 properties: " + p2);
}

for(p2 in book1){
    if(!book1.hasOwnProperty(p2)) continue;
    console.log("book1 NON inherited properties: " + p2);
}
//ECMAscript5 alternative
console.log("Using Object.keys()" + Object.keys(book1));


function inherit(p){
    if(p == null)
        throw TypeError();                          //p must be a non-null object.
    if(Object.create)                               // If Object.create() is defined...
        return Object.create(p);                    //then just use it.
    var t = typeof p;                               // Otherwise do some more type checking
    if (t !== "object" && t !== "function") throw TypeError();
    function f() {};                                // Define a dummy constructor function.
    f.prototype = p;                                // Set its prototype property to p.
    return new f();                                 // Use f() to create an "heir" of p.

}