Running a PhantomJS script with arguments

In this recipe, we will learn how to run a PhantomJS script with additional arguments that are passed into the script for evaluation. Note that these are arguments passed into the execution context and are not command-line arguments for the PhantomJS runtime itself.

Getting ready

To run this recipe, we will need a script to run with PhantomJS; the script in this recipe is available in the downloadable code repository as recipe04.js under chapter01. If we run the provided example script, we must change to the root directory for the book's sample code. Lastly, we will need the arguments we wish to pass into the script.

How to do it…

Given the following script:

if (phantom.args.length === 0) {
  console.log('No arguments were passed in.');
} else {
  phantom.args.forEach(function(arg, index) {
    console.log('[' + index + '] ' + arg);
  });
}

phantom.exit();

Enter the following command at the command line:

phantomjs chapter01/recipe04.js foo bar "boo baa"

We will see the following results printed in the terminal:

[0] foo
[1] bar
[2] boo baa

How it works…

Our preceding example script performs the following actions:

1. It checks the length of the phantom.args array and prints a message if that array is empty.
2. If the phantom.args array is not empty, we iterate over the items in the array, printing their index followed by the value of the argument itself.
3. Lastly, we exit from the PhantomJS runtime using phantom.exit.

As we discussed in the Running a PhantomJS script recipe, PhantomJS will attempt to evaluate and execute the first unrecognized argument as though it were a valid JavaScript file. But what does PhantomJS do with all of the arguments after that?

The answer is that they are collected into the phantom.args array as string values. Each argument after the script name goes into this array. Note that phantom.args does not include the script name itself. Instead, PhantomJS records that in the read-only phantom.scriptName property.

There's more…

It is worth noting that both phantom.args and phantom.scriptName are both marked as deprecated in the API documentation. As such, usage of both of these properties is discouraged. Although using them for quick one-off or exploratory scripts is fine, neither of these properties should go into any library that we intend to maintain or distribute.

Wherever possible, we should use the system.args array (from the system module) instead of phantom.args and phantom.scriptName.

Tip

When in doubt, check the PhantomJS project website and its documentation at http://phantomjs.org/api/. It is actively maintained, and as such will contain up-to-date information about the preferred APIs.

See also

• The Inspecting command-line arguments recipe in Chapter 2, PhantomJS Core Modules