Book Image

JavaScript and JSON Essentials

By : Sai S Sriparasa
Book Image

JavaScript and JSON Essentials

By: Sai S Sriparasa

Overview of this book

The exchange of data over the Internet has been carried out since its inception. Delimiter-separated lists such as CSV and tag-separated languages such as XML are very popular, yet they are considered to be verbose by a section of developers. JSON (JavaScript Object Notation) is a lightweight text-based code to create objects to transfer data over the Internet. It is a data exchange format that is human-readable (like XML, but without the markup around your actual payload) and its syntax is a subset of the JavaScript language that was standardized in 1999. JavaScript and JSON Essentials is a step-by-step guide that will introduce you to JSON and help you understand how the lightweight JSON data format can be used in different ways either to store data locally or to transfer data over the Internet. This book will teach you how to use JSON effectively with JavaScript. This book begins with a brief refresher course on JavaScript before taking you through how JSON data can be transferred via synchronous, asynchronous, and cross-domain asynchronous HTTP calls. JSON is not just about data transfer; this book throws light on the alternate implementations of JSON as well. You will learn the data types that JavaScript uses and how those data types can be used in JSON. You will go through the concepts of how to create, update, parse, and delete a JSON object. You will also look at the different techniques of loading a JSON file onto a web page, how to use jQuery to traverse through an object, and how to perform access operations. You will also go over a few resources that will make debugging JSON quick and easy.
Table of Contents (15 chapters)


Variables are good to hold single values, but for cases where a variable should contain multiple values, we would have to rely on arrays. A JavaScript array is a collection of items arranged in an order, according to their index. Each item, in the array, is an element and has an index, which is used to access that element. Arrays are like a bookshelf that holds more than one book; each book having its unique location. Arrays are declared using the array literal notation [].

Let us look at a simple array declaration:


Arrays in JavaScript are zero based.

Let us initialize the array:

To access the value of a specific element, the reference index of that element is used. Once the reference index is identified, it can be outputted using the alert statement, as shown in the following screenshot:

Unlike variables, arrays are not typed, therefore, they can contain various types of data, as shown in the following screenshot:

A much more complex example of a JavaScript array is a multidimensional array, where there is a combination of arrays inside an array, as seen in the following screenshot:

To retrieve an element from a multidimensional array, we would have to use as many indexes as the levels in that array. If the multidimensional array contains an array that has the values that we want to access, we will have to choose the index where the array element exists, and then choose the index of the value inside the array that we are searching for. To retrieve the string Three from the multidimensionalArray example, we will have to first locate the index of the array containing the value Three, and then find the index of the value Three inside that array. This is shown as follows:


The second way of declaring an array is by using the Array class.

var bookshelf = new Array()