• Choose a category
• All
• Classic-Fiction

myLibrary.books=[predefinedBook1,predefinedBook2,predefinedBook3];

And to build a JavaScript Object, we use curly braces, with each value written as a key:value pair:

myLibrary.books={

bestSeller : predefinedBook1,

cookbook : predefinedBook2,

spaceFiller : predefinedBook3

};

In both notations, extra white space is ignored, allowing us to pretty-print for clarity. Keys can also have spaces in them, and can be quoted in the JSON notation, for example:

"Best Seller" : predefinedBook1,

We can nest JSON notations to create one-line definitions of complex object hierarchies (albeit rather a long line): var myLibrary={

location : "my house",

keywords : [ "root vegetables", "turnip", "tedium" ], books: [

{

title : "Turnip Cultivation through the Ages",

authors : [

{ name: "Jim Brown", age: 9 },

{ name: "Dick Turnip", age: 312 }

],

publicationDate : "long ago"

},

{

title : "Turnip Cultivation through the Ages, vol. 2", Licensed to jonathan zheng

Objects in JavaScript

595

authors : [

{ name: "Jim Brown", age: 35 }

],

publicationDate : new Date(1605,11,05)

}

]

};

I have assigned three properties to the myLibrary object here: location is a simple string, keywords is a numerical list of strings, and books a numerically indexed list of objects, each with a title (a string), a publication date (a JavaScript Date object in one case and a string in the other), and a list of authors (an array). Each author is represented by a name and age parameter. JSON has provided us with a concise mechanism for creating this information in a single pass, something that would otherwise have taken many lines of code (and greater bandwidth). Sharp-eyed readers will have noted that we populated the publication date for the second book using a JavaScript Date object. In assigning the value we can use any JavaScript code, in fact, even a function that we defined ourselves: function gunpowderPlot(){

return new Date(1605,11,05);

}

var volNum=2;

var turnipVol2={

title : "Turnip Cultivation through the Ages, vol. "

+volNum,

authors : [

{ name: "Jim Brown", age: 35 }

],

publicationDate : gunpowderPlot()

}

]

};

Here the title of the book is calculated dynamically by an inline expression, and the publicationDate is set to the return value from a predefined function. In the previous example, we defined a function gunpowderPlot() that was evaluated at the time the object was created. We can also define member functions for our JSON-invoked objects, which can be invoked later by the object: var turnipVol2={

title : "Turnip Cultivation through the Ages, vol. "+volNum, authors : [

{ name: "Jim Brown", age: 35 }

],

Licensed to jonathan zheng

596

APPENDIX B

JavaScript for object-oriented programmers

publicationDate : gunpowderPlot()

}

],

summarize:function(len){

if (!len){ len=7; }

var summary=this.title+" by "

+this.authors[0].name

+" and his cronies is very boring. Z";

for (var i=0;isummary+="z";

}

alert(summary);

}

};

...

turnipVol2.summarize(6);

The summarize() function has all the features of a standard JavaScript function, such as parameters and a context object identified by the keyword this. Indeed, once the object is created, it is just another JavaScript object, and we can mix and match the JavaScript and JSON notations as we please. We can use JavaScript to fine-tune an object declared in JSON:

var numbers={ one:1, two:2, three:3 };

numbers.five=5;

We initially define an object using JSON syntax and then add to it using plain JavaScript. Equally, we can extend our JavaScript-created objects using JSON: var cookbook=new Object();

cookbook.pageCount=321;

cookbook.author={

firstName: "Harry",

secondName: "Christmas",

birthdate: new Date(1900,2,29),

interests: ["cheese","whistling",

"history of lighthouse keeping"]

};

With the built-in JavaScript Object and Array classes and the JSON notation, we can build object hierarchies as complicated as we like, and we could