Enforcing coding rules in your team with JSCS

28 January 2014

Enforcing coding rules in a team is hard, and most of the time it ends with a very long documentation lost on the company wiki which nobody reads. You can also check the coding rules during code reviews and make the apropriate corrections if needed but it can be very painful and time consuming.

According to me, the only solution is to rely on some tools to check the code and warn the developper if he do not follow the rules. It can be a simple warning as it can totally forbid him to push some code, it is up to you to choose how strict you want to be.

My tool of choice for this is JSCS (for JavaScript Code Style checker). We'll see how to integrate it in your team tools and in your workflow.

Installing JSCS

JSCS is a simple npm module to install globaly.

npm install jscs -g

You have now the JSCS tool available globaly.

To check your code JSCS will need a configuration file named .jscs.json at the root of your project. This file will contain all the rules your code must follow.

As an example you can check the jQuery .jscs.json configuration file bellow:

    "requireCurlyBraces": [ "if", "else", "for", "while", "do" ],
    "requireSpaceAfterKeywords": [ "if", "else", "for", "while", "do", "switch", "return" ],
    "requireSpacesInFunctionExpression": {
        "beforeOpeningCurlyBrace": true
    "disallowSpacesInFunctionExpression": {
        "beforeOpeningRoundBrace": true
    "requireMultipleVarDecl": true,
    "requireSpacesInsideObjectBrackets": "all",
    "requireSpacesInsideArrayBrackets": "all",
    "disallowLeftStickedOperators": [ "?", "-", "/", "*", "=", "==", "===", "!=", "!==", ">", ">=", "<", "<=" ],
    "disallowRightStickedOperators": [ "?", "/", "*", ":", "=", "==", "===", "!=", "!==", ">", ">=", "<", "<="],
    "requireSpaceBeforeBinaryOperators": ["+", "-", "/", "*", "=", "==", "===", "!=", "!=="],
    "disallowSpaceAfterPrefixUnaryOperators": ["++", "--", "+", "-"],
    "disallowSpaceBeforePostfixUnaryOperators": ["++", "--"],
    "requireRightStickedOperators": [ "!" ],
    "requireLeftStickedOperators": [ "," ],
    "disallowKeywords": [ "with" ],
    "disallowMultipleLineBreaks": true,
    "disallowKeywordsOnNewLine": [ "else" ],
    "requireLineFeedAtFileEnd": true,
    "disallowSpaceAfterObjectKeys": true,
    "validateLineBreaks": "LF"

These rules enforce curly braces after if statements, disallow the use of with, enforce Unix line ending and so on. You can found the rules list and their meaning in the JSCS Readme.

When you have finished to play with the rules, put your .jscs.json configuration file at the root of your project.

You can already check your code by typing this command at the root of your project:

jscs path/to/my/script.js


jscs .

to check the whole project (. is the current directory).

You should get something like this:

JSCS from the command line

Great ! You can now check your code with JSCS ! But for now this is not very convenient.

Intregrating JSCS in Sublime Text

For this you will need Sublime Text 3 with Package Control.

First you will need to install SublimeLinter using Package Control (follow the SublimeLinter documentation if you are not sure about the procedure).

Then, the same way you've installed SublimeLinter, search for the package SublimeLinter-jscs in Package Control and install it.

And... you've done ! Now if you try to open your project JavaScript files in Sublime Text you should have your errors highlighted by SublimeLinter.

Highlighting coding style errors with SublimeLinter-jscs

If you are not using Sublime Text as text editor (shame on you !) JSCS has also some plugins for Vim, Brackets and LightTable.

If you are using none of those, keep reading ;)

Adding JSCS as a Grunt task

The Sublime Text plugin is great but if you have some teamates that do not use an editor with a JSCS plugin and keep pushing some unchecked code all your hard work will be in vain.

Here's enter Grunt.

If you are already using Grunt it will be a simple task to add to your tasklist.

Just install the grunt-jscs-checker npm package:

npm install grunt-jscs-checker --save-dev

And add a jscs entry in your Gruntfile.js:

jscs: {
  src: "path/to/my/*.js"

Read the Readme for more options.

Then run the task to check the whole project:

JSCS from Grunt

Not very different from the command line, but we can now configure Grunt to run it with other tasks, like your tests:

grunt.registerTask('test', ['jscs', 'jasmine']);

This way you will check your project coding style besides to the tests compliance.

(If you are using Gulp instead of Grunt you can use the gulp-jscs task)

Adding JSCS as a Git pre-commit hook

Ok, now we need to be sure JSCS will be run before every commit. A way to do this is to use grunt-githooks that will easily bind your Grunt tasks to Git hooks.

Like before, install the grunt-githooks npm package:

npm install grunt-githooks --save-dev

And add a githooks entry in your Gruntfile.js:

githooks: {
  all: {
    'pre-commit': 'test'

Run grunt githooks to bind the tasks and you're done.

From now, next time you will commit the test task will run and if it finish in error (error in the coding style or in the tests) the commit will be aborded.

JSCS as a Git pre-commit hook

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