JSLint in your workflow

Primer

JSLint is a code validation tool for JavaScript

Using it will help ensure JavaScript on a project is produced in a consistent way that avoids syntax errors.

The option to 'JSLint' a JavaScript file is everywhere but the options that it is being run under are usually not shown. This means you're validating your code against invisible settings. It also means members of a team can be validating their JavaScript against settings different to yours, which is dangerous.

Goal

Be able to lint code against the same options on everyone's IDE across the project

A bit more specifically, we need to run a set version of JSLint, with set options and we need to be able to run this on any OS and with any IDE.

Programs used

• Java (Java Developer Kit (JDK) or Java Runtime Executable (JRE) - used to run Java programs)
• JSLint4Java - a Java program used to run jslint
• Rhino - Mozilla's Java implementation of JavaScript. Can run any JavaScript program.
• JSLint

Using Java on your computer

Check if you have a version of Java on your computer:

Windows

1. Go to Start menu
2. Go to 'Run'
3. Type 'cmd' to enter the command line
4. Type 'java -version'

Mac

1. Open the Terminal App (in Applications -> Utilities)
2. Type 'java -version'

If you get:'java is not recognised as an internal or external command, operable program or batch file' you don't have Java.

If you get output that starts 'java version' you have it.

If you haven't got a version of java on your computer, download the JRE or JDK from Oracle

On both Windows & Mac, the installer will take care of everything to do with the installation. On Mac, installing a new version of Java will not always update your core version. If this happens, use the Java Preferences App (Applications -> Utilities -> Java Preferences App) to switch versions.

Running JSLint through Java

We are interested in running JSLint using Java because:

1. Java is supported cross-platform and cross-OS
2. Running JSLint through a non-browser-based program allows a lot of flexibility.
3. Jars are supported by most Continuous Integration Processes.

So, in short, what we are trying to do is run a program that checks a file against JSLint validation and outputs the results of this. There are a few options of how to do this.

Options for doing this

The first time I tried this (under the tutelage of @agentdeal using Mozilla's Rhino, a Java program that runs JavaScript programs. It does this by running jslint.js and sending it the JavaScript file you are testing as a parameter.

java -jar js.jar jslint.js filetotest.js

The results are produced by Rhino as standard output meaning it's up to you what you do with them.

Even now this is still a good and solid method and benefits from being very simple and also by no part of its process hidden. It also doesn't pack JSLint into the jar meaning you can grab the latest version from Douglas Crockford's repo on Github

If you prefer a jar with all this as options, rather than file dependancies (which is a lost less hassle to plug into your Maven or Ant config file, you may like JSLint4Java.

I'm not going to tell you which to chose but I do list each approach on separate pages:

• Rhino
• JSLint4Java

I personally prefer to leave the options and globals settings in the JavaScript files themselves so people can see what their code is being validated against.

A word of caution

How ever you go about running it JSLint can, to quote Mr Crockford, Hurt your feelings with its bluntness. This is what you want (clarity) but it will only work if you don't confuse this directness your own set up errors.

So make sure the options you are setting confirm the idea of valid code your developers are working to and be aware that any options you don't set values for will inherit them from the version of jslint.js you are using.

Also ensure you use an external version of jslint.js, preferably the latest from github. Without specifying this with JSlint4Java you will be using the one baked into the jar.