JSCoverage-style instrumentation for CoffeeScript files.

npm install coffee-coverage
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Benbria CoffeeCoverage

Compiles .coffee files to .js files, and adds JSCoverage style instrumnetation for the original coffee script source.


What it Does

Benbria CoffeeCoverage takes a collection of .coffee files, and produces .js files which have been instrumented to record how many times each line is executed. Given a file "":

console.log "Hello World"

It produces output that looks something like this (edited slightly for brevity and readability):

// coffeeCoverage generated initialization
if (! _$jscoverage[""]) {
    _$jscoverage[""] = [];
    _$jscoverage[""][1] = 0;
_$jscoverage[""].source = ["console.log \"Hello World\"", ""];

(function() {

  _$jscoverage[""][1]++; // Count that we're executing line #1
  console.log("Hello World");


The output is intentionally similar to that of JSCoverage, so that your source can be used with existing coverage-analysis tools.

Installation and a Quick Intro

Install with:

npm install -g coffee-coverage

Given a directory "source" full of .coffee files, run:

coffeeCoverage ./source ./dest

This will recursively find all the .coffee files in the "source" directory, and produce .js files in the "dest" directory. Note that you can compile in-place with:

coffeeCoverage ./source ./source

How it Works

See the Design page on the Wiki.

Using with Mocha and Node.js

Dynamic Compilation

There are two ways to use coffeeCoverage as part of your unit tests. First, if you run your tests directly on your .coffee files, you can register coffeeCoverage to dynamically compile .coffee (and even ._coffee if you're using streamlinejs) files. For example, create a "register-handlers.js":

# If you're using with streamline, you *must* register streamline first:

#  Register coffee-coverage if coverage is enabled.
if(process.env.COVERAGE) {
        path: 'abbr',
        basePath: __dirname,
        exclude: ['/test', '/node_modules', '/.git'],
        initAll: true,
        streamlinejs: true

Note we set the "basePath" to the root of our project. This can be a path which is relative to __dirname (e.g. __dirname + "/..").

Note that streamline support is "experimental" right now (i.e. it might break at any moment because we're using undocumented features in streamlinejs) so to turn it on, you have to explicitly pass 'streamlinejs: true' as an option.

Then, run your tests:

COVERAGE=true mocha --require register-handlers.js --reporter html-cov ...

Static Compilation

Alternatively, you can use coffeeCoverage to statically compile your code with instrumentation:

# Compile everything except the test directory with coffeeCoverage
coffeeCoverage --initfile ./lib/init.js --exclude test --path abbr ./src ./lib
# Compile the test directory with regular coffee-script
coffee -o ./lib/test ./src/test

This also writes an "lib/init.js" which initializes all the execution counts to 0. This is handy, because otherwise if we never require a given module, that module's counts won't show up at all in the code coverage report, which might overly inflate our code coverage percentage. Next we run our tests:

mocha --require ./lib/init.js --reporter html-cov ./lib/test/*

Static compilation does not currently support streamline.

Some Weirdness with Line Numbers

This snippet of CoffeeScript:

if x then y() \
     else z()

gets compile to this snippet of JavaScript:

if (x) {
} else {

We have three statements we could annotate here; the "if" itself, the call to y, and the call to z. The problem is that both the "if" an the call to "y()" are on the same line of CoffeeScript source. If we annotate both the "if" and the "y()", then if x is true, we will count two executions of the first line of the CoffeeScript, even though we've only run this chunk of CoffeeScript once.

CoffeeCoverage tries to work around this by only instrumenting the first statement it finds on a line, so in the above example, we'd annotate the "if" and the "z()", but not the "y()".

Also, it's worth noting a minor difference in the way coffee-coverage compiles statements. The following coffee code:

if x
else if y

Would normally compile to:

if(x) {
} else if(y) {

coffeeCoverage will instead compile this to:

if(x) {
} else {
  if(y) {

because otherwise it would be unable to annotate the if(y) statement.

Detailed Usage

Usage: coffeeCoverage [-h] [-v] [-c name] [-e filenames] [-i initfile] [--path pathtype] src dest

src and dest are the source file or directory and destination file or directory, respectively. If src is a .coffee file, then coffeecoverage will instrument the file and write the result to dest (e.g. coffeeCoverage a.js.) If src is a directory, then coffeecoverage will recursively walk through src finding .coffee files, and writing them into the dest, creating any subdirectories in dest as required. If src and dest are the same directory, then all the .coffee files in src will have .js files written alongside them.

Optional arguments:

-c, --coverageVar

By default, coffeecoverage will instrument source files with the global variable "_$jscoverage". This is done to mimic JSCoverage. You can rename this variable by using this option.

-i, --initfile

Specifies an "initfile" which all global initalization is written to. This is handy for testing with mocha. If you require the initfile, then mocha reports will show coverage of all files in your project, even files which were never required anywhere.

-e, --exclude

Gives a comma delimited list of files and directories to exclude from processing. This defaults to 'node_modules,.git', since neither of these are directories you probably want to be instrumenting. If you want to also exclude your "test" directory, you might run coffeeCoverage with:

coffeeCoverage --exclude 'node_modules,.git,test' ...


Path can be given one of three different parameters:

  • none is the default - if coffeeCoverage reads a file from "src/models/", then the instrumented code will use the filename "". This works well provided you don't reuse filenames elsewhere in your code. Note that if there is a name collision between two files in different subdirectories, coffeecoverage will append a something to the end of one to make it unique, otherwise coverage data from one file would interfere with data from another.
  • abbr will use abbreviated path names; a file from "src/models/" will be instrumented as "s/m/".
  • relative will use the full relative pathname; "src/models/".

Paths are always relative to the src directory provided on the command line.

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