You may also want to build your own binaries by compiling PhantomJS from source. Sources are hosted in the Github server at https://github.com/ariya/phantomjs.

Before you start downloading sources, you will need these tools installed on your workspace:

The PhantomJS team is always trying to find the optimal way to build the sources, and the build instructions are frequently modified. To build PhantomJS properly, you must follow the steps found here: http://phantomjs.org/build.html.

If you are not planning to hack into PhantomJS code and develop new features, then it is best to download the pre-packaged binaries.

Now, let's see how PhantomJS's magic works. It is a command-line-based application, so we need to execute it in an OS terminal or console. The PhantomJS package contains a series of files and comes with one main executable file, which is named phantomjs.

Open your terminal and then navigate to your PhantomJS bin folder. In the prompt, execute phantomjs without any arguments.

Running PhantomJS without any arguments will give you an interactive prompt that is similar to the JavaScript debug console you could find in any modern browser. In this interactive prompt, we can execute JavaScript code line by line. This functionality is very useful for debugging or testing code before you actually build your script.

Say "Hello Ghost!" to PhantomJS using the interactive prompt. Using console.log will output any type of data to the output console of a JavaScript interpreter.

phantomjs> console.log("Hello Ghost!")
Hello Ghost!
undefined
phantomjs>

See? It is simple. Just like coding any JavaScript. But wait. What is that undefined message just after the Hello Ghost! message? That is not an error. It is just how the interactive mode behaves. Each call is expected to return data just like any ordinary function call and it also automatically outputs the data value to the output stream.

Since the console.log command does not return any value, the message is undefined. If we issue an assignment to a variable command, the following output will be displayed:

phantomjs> name = "Tara"
{}
phantomjs>

The assignment to a variable will take place and the result of the operation will be displayed. Because it is in the form of a string literal, the undefined message will not be displayed. The interactive mode is similar to a long-running script; any variable or function you define will be loaded into the memory buffer and can be accessed anytime during the session. So, based on our preceding example, the name variable can also be displayed by referencing it.

phantomjs> name = "Tara"
"Tara"
phantomjs> name
"Tara"
phantomjs> name + " and Cecil"
"Tara and Cecil"
phantomjs>

We can even use the variable with another operation as seen in the preceding lines of code. However, any operation's result that is not assigned to a variable will be available only during the execution of the line. The operation that concatenates the name variable with another string literal will be performed, and the resulting string will be displayed in the console but will not be kept in memory.

Objects can also be accessed within the interactive mode, and one of the most commonly used objects is phantom. Try typing phantom in the prompt and you will get the following output:

phantomjs> phantom
{
   "clearCookies": "[Function]",
   "deleteCookie": "[Function]",
   "addCookie": "[Function]",
   "injectJs": "[Function]",
   "debugExit": "[Function]",
   "exit": "[Function]",
   "cookies": [],
   "cookiesEnabled": true,
   "version": {
      "major": 1,
      "minor": 7,
      "patch": 0
   },
   "scriptName": "",
   "outputEncoding": "UTF-8",
   "libraryPath": "/Users/Aries/phantomjs/bin",
   "defaultPageSettings": {
      "XSSAuditingEnabled": false,
      "javascriptCanCloseWindows": true,
      "javascriptCanOpenWindows": true,
      "javascriptEnabled": true,
      "loadImages": true,
      "localToRemoteUrlAccessEnabled": false,
      "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X)AppleWebKit/534.34 (KHTML, like Gecko) PhantomJS/1.7.0Safari/534.34",
      "webSecurityEnabled": true
   },
   "args": []
}
phantomjs>

PhantomJS displays the content of the object when used in the interactive prompt, and even its own phantom object can be referenced. You may also observe that the object is displayed in the form of JSON and details every attribute of the object except for the function definition. Using this approach, we can also examine each and every object, and we will be able to know what the exposed attributes and available functions are.

Let's try using one of the most important functions available in the phantom object: the exit() function. This function will enable us to quit PhantomJS and return to the caller or to the underlying operating system.

phantomjs> phantom.exit()
$

This function signals the application to exit with a return code of zero or normal and without errors. Passing a numeric value as an argument of the exit() function denotes the error code to be passed back to the caller. This is helpful when trying to write scripts that need to verify if the execution was successful or if an error occurred and what type of error it was.

If we trap the error code in a shell script, it will look as follows:

#!/bin/bash
bin/phantomjs
OUT=$?
if [ $OUT -eq 0 ];then
   echo "Done."
else
   echo "Ooops! Failed.!"
fi

In the preceding lines of code, right after calling phantomjs, we capture the error code coming from the application using the $? function. We assign that to an OUT variable and then perform a test on it in the succeeding lines. If the error is equal to zero, then we display Done; otherwise, we say that the call failed.

$ ./trapme.sh 
phantomjs> phantom.exit(0)
undefined
Done.
$ ./trapme.sh 
phantomjs> phantom.exit(1)
undefined
Ooops! Failed.!
$

Use the interactive mode to experiment with the PhantomJS API.

Before we begin creating PhantomJS scripts, we first need to make a quick roundup of the PhantomJS JavaScript API.

PhantomJS runs JavaScript and comes with a JavaScript API to make your life easy. It extends the standard JavaScript API and adds richer layers of capabilities, such as allowing us access to the underlying file system, ease of access and manipulation of DOM objects, system and environment variable gathering. It even gives us the ability to inject custom scripts into the web page.

But, be warned. PhantomJS is a very active community, and every now and then, changes are being introduced. New APIs and objects are being added, but of course, there are few items that are being changed, and ultimately some of them become deprecated or are totally removed. The PhantomJS website has a full list of all the functions and syntax, and has proper tagging for deprecated functions. We should visit it regularly to check for upcoming updates so that we can adjust appropriately in our codes.

The phantom object is your reference to PhantomJS within your scripts that allows you to access certain properties and provides functionality that affects the entire script (such as quitting the application as previously mentioned.) The phantom object can be directly referenced anywhere in the script and does not need to be explicitly imported. You may also access it as a child of the global window object.

The phantom object allows access to relevant data, such as cookies and library paths. If we want to import or inject third-party JavaScript libraries, such as jQuery, we can do that using the phantom object. We can also create a "catch all" event handler for errors using the onError event of the phantom object.

PhantomJS not only allows us to harness the power of JavaScript but also gives us a very useful API. Each day, more and more contributors are enhancing this API, giving us more options and easier ways to solve real problems. We will learn more about these APIs as we continue our journey learning about PhantomJS.

There are a few command-line arguments that we need to understand before plunging into writing PhantomJS scripts. The syntax of the PhantomJS argument is:

phantomjs [switches] [options] [script] [argument [argument [...]]]

All of the arguments are optional. Using the command without arguments will bring up the interactive mode.

phantomjs /scripts/chapter1.js

phantomjs --debug=yes /scripts/chapter1.js

phantomjs --cookie-file=/scripts/cookies.txt /scripts/chapter1.js

We know how to write JavaScript, and now we know that there are several PhantomJS JavaScript APIs and objects. We also have learned the basics of the PhantomJS command-line arguments. We are now ready to create our own scripts.

We will create a simple script to load a site and then display the title of the page when loaded successfully. Finally, we will exit. If the page fails to load, we will log some message to the console.

var page = require('webpage').create();
page.open("http://www.packtpub.com", function(status) {
   if ( status === "success" ) {
      console.log(page.title); 
   } else {
      console.log("Page failed to load."); 
   }
   phantom.exit(0);
});

The preceding PhantomJS script is very simple. First, we import the webpage module, create an instance of the webpage object, and assign it to a variable named page.

The page variable now holds an instance of the webpage module where an open function is available. Next, we instructed PhantomJS through the webpage instance to open and load the URL. The second parameter of the open function is a function callback definition that will be executed upon completion of the opening of the URL. Inside the definition, we check if the status is "success", and if it is, the page is loaded, and then we will display the title of the page. Then, we call the exit function to terminate the script. Let's save this code snippet as helloweb.js and execute it by passing the filename as our first argument to the phantomjs binary.