Running JSLint using Mozilla Rhino

Note: this post assumes you already have a version of Java installed on your OS. If not, refer to this post for how to get it.

Mozilla's Rhino is a Java program that runs JavaScript. What this means to you is you can use it to run JavaScript programs outside of the browser, like Python, Perl, PHP, etc...

Because we are trying to run a JavaScript program (JSLint) on the command-line that takes arguments and outputs results in text form, it's quite useful.

Installation

Rhino takes a little longer to install, mainly because the downloaded files then need building. What I mean by this is that some of the installation process is done by a build tool called ant.

This sounds excessive, but if you have a Mac you'll probably already have it. If you don't, you should, it's amazing. (It's also used by many Java programs as part of their installation so you'll need it in future.)

To check if you have it, try typing ant on either your commmand-line (Windows) or in your Terminal (Mac).

If you get this: Buildfile: build.xml does not exist!

...then you have it. (Ant uses build.xml as its default configuration file so this message is just saying there isn't one.)

If you get: ant is not recognised as an internal or external command, operable program or batch file ...or a similar message then you haven't got Ant.

Installing Ant

Getting the files

If you're on Windows, it's a good idea at this stage to create a folder called 'Apache Software Foundation' in your C:\Program FIles folder. (This is just for organisational purposes, to keep all software you may use from Apache in one place.)

Download the latest .zip file of Apache Ant from here (It will be called something like apache-ant-1.8.2-bin.zip)

On Windows, extract it into the 'Apache Software Foundation' folder you made before. This should create a folder called what the .zip is but without the -bin.zip bit. Something like 'apache-ant-1.8.2'.

On Mac it's better to keep it somewhere like /usr/local/bin so you should do the following in your Terminal app (Applications -> Utilities -> Terminal).

Assuming you downloaded it to your Downloads folder, navigate to it like so: cd Downloads (This assumes this is your 1st command & therefore being executed in your home folder).

Type mv apache-ant-1.8.2.zip /usr/bin/apache-ant-1.8.2.zip to move it to the /usr/bin folder.

Type: tar -xvf /usr/bin/apache-ant-1.8.2.zip ...to extract the zip archive into a folder of the same name, using the tar utility program. Options used are to 'extract', 'use a verbose style to report the results' & 'use the file specified by the given path'.

Type: rm /usr/bin/apache-ant-1.8.2.zip ...to remove the original zip file.

If you have issues with any of the commands above you may need to preface them with the sudo command, i.e. sudo tar -xvf /usr/bin/apache-ant-1.8.2.zip

Note: do not use the sudo prefix without understanding it, it removes safe-guards to any commands you run.

Installation

In Windows, in your explorer window, copy the path to this folder (i.e. C:\Program Files\Apache Software Foundation\apache-ant-1.8.2)

Ant uses enviroment variables (variables that are available to all programs on an OS, used point to common resources) to work.

On Windows, these are set up like so:

1. Go to your desktop and right-click on the 'My Computer' icon.
2. Select 'properties' on the menu.
3. Click on the 'Advanced' tab.
4. Inside this tab there is a button called 'Environment Variables'. Click on it to bring up another menu.
5. In the section at the bottom called 'System variables', click the 'New' button.
6. Enter the variable name as ANT_HOME and the variable value as the path to your ant folder you copied before. (i.e. C:\Program Files\Apache Software Foundation\apache-ant-1.8.2) This creates an environment variable pointing to where ant is on your system.
7. In the section at the bottom called 'System variables' scroll the list until you find an entry called 'Path' and click on it to select.
8. Click the 'Edit' button and add this to the end: ;%ANT_HOME%\bin. The semi-colon adds a new sub-section to the path, %ANT_HOME% uses the enviroment variable you created and adding \bin to the end. So you're effectively adding C:\Program Files\Apache Software Foundation\apache-ant-1.8.2\bin to it.*

* This means that when you type 'ant' at the command prompt, Windows will search the local directory for a program called 'ant' and when it doesn't find one will search all folders listed in the Path string. As the bin folder (inside your ant folder) is now one of these, it will look inside there and run the 'ant' program.

Note: Running the JDK/JRE installer should have added an environment variable called JAVA_HOME. If you don't have this, you'll need to add it, pointing to the JDK or JRE folder in C:\Program Files\Java, i.e. C:\Program Files\Java\jdk1.7.0'

On Mac, open the Terminal app & type these commands:

export ANT_HOME=/usr/bin/apache-ant-1.8.2

export PATH=${PATH};${ANT_HOME}/bin

In the above commands, we are assuming your Apache Ant folder is as we specified above & we are then adding that environment variable to your path.

If the ANT_HOME environment variable is set to /usr/bin/apache-ant-1.8.2 then PATH=${PATH};${ANT_HOME}/bin is adding /usr/bin/apache-ant-1.8.2/bin to the end of the PATH variable string.

After all this, close and reopen the command prompt and type ant. If you get Buildfile: build.xml does not exist! ...you now have ant. Otherwise, check the stages above to make sure all is set up ok.

Installing Rhino

You can get the files for Rhino from here.

Place the zip where ever you want the Rhino program to sit (i.e. on Windows it might sit in C:\Program Files\Java). Unzipping the file should leave you with a similarly-named folder, for example, something like C:\Program Files\Java\Rhino1_7R3 from Rhino1_7R3.zip.

Now use either command-line (on Windows) or Terminal (on Mac) to move into the new folder:

(Windows) cd C:\Program Files\Java\Rhino1_7R3

(Mac) cd /usr/local/bin/Rhino1_7R3

Type ant and Ant should build Rhino. If it works you should get no errors and be left with a file called js.jar in the folder.

Using Rhino

Rhino runs like any other jar file, taking the JavaScript file you want to run as the 1st argument and any following arguments are passed to the JavaScript file. So this:

java -jar C:\Program Files\Java\Rhino1_7R3\js.jar fulljslint.js filetotest.js

Uses Java to run the C:\Program Files\Java\Rhino1_7R3\js.jar jar program, sending it the JavaScript file fulljslint.js and sending that file filetotest.js as its first parameter.

Now hold on a minute

You may have spotted that there's something I've left out. I've not explained about the file you're sending to Rhino (fulljslint.js). It turns out you can't just send Rhino jslint.js and there's a good reason for this.

Rhino will run any JavaScript you send it but that's all it will do. jslint.js is pretty simple, it takes 2 arguments: the JavaScript file to validate as a string and an object of options to validate against. It can't output the results to the command-line/terminal, or anything else you tell it to because it doesn't know how (JavaScript programs generally have no access to the output stream). So fulljslint.js is actually jslint.js with some extra code at the end to print the results it produces.

I made a version of fulljslint.js with the latest version of jslint.js from github (dated 2011-07-19) here.

If you want to update the version of jslint.js in it, just get the version you need and add this file on the end.

In closing

Well done you made it to the end, that took ages didn't it? In getting this far you have:

• Got Apache ant on your machine which is brilliant.
• Got Rhino, which can be used to run any JavaScript file outside of the browser.
• Understand how it all works so you can change it.

A quick note. I got the Rhino code via http://hustoknow.blogspot.com/2011/02/jslint-and-rhino-support.html so thanks to Roger Hu for his work on this.