WebAssembly in Action

Author of the book "WebAssembly in Action"
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The book's original source code can be downloaded from the Manning website and GitHub. The GitHub repository includes an updated-code branch that has been adjusted to work with the latest version of Emscripten (currently version 3.1.44).

Friday, September 17, 2010

JSON Overview

When you have two components that need to talk to each other (over the internet for example) you need some way to pass data back and forth.

Up until recently XML was the solution that was often chosen as the data transmission format. Often times, the communication involved a very verbose form of XML known as SOAP.

More recently a new format has arrived that has begun to replace XML as the data transmission format of choice, especially when dealing with web sites and web applications, called JSON.

JSON stands for JavaScript Object Notation and is a lightweight data-interchange format that is easy for humans to read and write and is easy for machines to generate and parse. (I paraphrased this paragraph some from: http://www.json.org/)

Most major programming languages have support for JSON in one way or another through libraries or, in some cases, built right in. RESTful services in .NET, for example, can return XML or JSON.

Initially I thought JSON was just for objects, as its name suggests, but it turns out that it can be used to represent two different structures:
  • an Object
  • or, an Array

Creating a JSON Object

A JSON Object is created by having an opening curly brace ({) followed by name/value pairs.

Each name/value pair is separated by a comma (,).

The name/value pair itself is separated by a colon (:).

The name is a string but the value can be a string, number, object, array, true, false, or null.
Being able to use an object for the value portion of a name/value pair opens possibilities such as nesting additional JSON objects within a JSON object or creating functions within the JSON object.

The JSON object is closed by using a closing curly brace (})

JSON objects are declared and initialized in one step and result in what’s known as a singleton object.
Being able to create a singleton object is not unique to JSON. You can cause a standard JavaScript class to be created as a singleton object but there is a bit more work involved to do so. The difference is that, with JSON, the object cannot be declared in one spot and then initialized later like a standard class can be.

The following is the simplest JSON object you can create:
var objObject = {};

The above example is simply shorthand for writing the following:
var objObject = new Object();

The following is an example of a JSON object created that has two properties FirstName and LastName with the values Sam and Smith respectively:
var objEmployee = {
"FirstName": "Sam",
"LastName": "Smith"

Using the new objEmployee object in JavaScript is simply a matter of using the dot operator to access the properties that were created as in the following example:
alert("The employee’s name is: " + objEmployee.FirstName + " " + objEmployee.LastName);

Creating a JSON Array

To create a JSON Array you use an opening square bracket ([) followed by comma separated values and closed by a closing square bracket (])

The simplest JSON Array that you can create is an empty array using the following syntax:
var arrArray = [];

The above example is simply shorthand for writing the following:
var arrArray = new Array();

The following is an example of creating an array containing three strings:
var arrArray = [

Creating a JSON Class

It totally depends on your needs if JSON is the right choice for you when it comes to creating classes.

Some people find JSON classes simpler and easier to read. I personally don’t see a big difference between the readability of a standard JavaScript class and a JSON class.

If you’re happy with all of your members and methods in a class being public, creating the class using JSON is a bit simpler especially since you don’t need to declare the class first and then initialize it later. This is because a JSON object/class is automatically initialized as soon as it’s declared resulting in what is known as a singleton object since you only get the one object per class declaration.

This automatic initialization when the JSON class has been declared has its uses like if you wanted to have a global namespace object that contains some helper methods and don’t want to require the developer of the page(s) to initialize the object first before using the methods (acts like global functions but contained in a more structured class).

A JSON class is constructed the same way a simple JSON object is created but instead of a simple variable or object, you use a function as the value portion of the name/value pair as in the following example:
var Employee = {
"FirstName": "Sam",
"LastName": "Smith",

// Our method to return the Employee's full name
"GetFullName": function () {
return (this.FirstName + " " + this.LastName);


Converting strings of JSON into JSON objects

When requesting JSON data from a server it usually gets returned as a string of text.

Whenever possible it is recommended that the parsing of a string into a JSON object be done using the native browser methods if the browser supports those methods.

Converting a string of JSON into a JSON object, using the native browser object, is as simple as the following:
var sJSON = "{ \"FirstName\": \"Sam\", \"LastName\": \"Smith\" }";

var objJSON = JSON.parse(sJSON);

alert("JSON object's data: " + objJSON.FirstName + " " + objJSON.LastName);

In Conclusion

JSON is an interesting technology that can simplify some tasks as well as help to reduce the amount of bandwidth used when transmitting data between components over the internet/intranet especially when compared to SOAP.

The large number of libraries and built-in functionality for JSON also makes passing data using this format much easier.


  1. Is your Employee class above de/serializable across the wire? In other words, if a client requests an Employee instance from a server, is the data 'and' behavior deserialized on the client? As with Java, the class definition would have to exist on both the client and server, right? I do this with Java objects, and just wondered if it's possible to do with Javascript.

  2. The data is passed as a string between the server and client.

    There is no built-in de/serialization that I'm aware of other than JSONP (script injection causing code to be downloaded and parsed by the browser...parsed code is then passed to the function you specified).

    To deserialize on the client using the browser's native object you pass the string received into JSON.parse(sStringReceived).

    To serialize an object on the client to be passed to the server, using the browser's native object, you pass the object into JSON.stringify(objJSON)

    Your server-side code would need to parse the received JSON data and map it to your server-side class object.

    On the client-side, the parsed JSON string becomes an object that you can start working with right away. You can map this data to your own class if you wish.

  3. can you provided a real time..

    Suryaprakash Raghuwanshi