karma-istanbul-preprocessor

A small preprocessor to help merge different instrumentation runners into an aggregate tool like karma-coverage.

Should you use this plugin?

Try the standard tools like karma-coverage or browserify-istanbul. Come here when you find you need to run both at the same time :-)

Installation

npm install --save-dev karma-istanbul-preprocessor

Usage

Add istanbul to your karma.conf.js like so:

// karma.conf.js
module.exports = function(config) {
  config.set({
      preprocessors: {
          // Source files that you want to add instrumentation for
          '**/*.js': ['istanbul'],
      },
  });

Now what?

This plugin does not display coverage or do anything other than add instrumentation. You still probably want to set up karma-coverage like normal, except do NOT add the coverage preprocessor.

Contributing

Open an issue or a PR, and we'll go from there.

Why?

For a bit more of a long-form answer: I was debugging into why generating HTML coverage was failing. It turns out that when you use karma-coverage, it keeps track of a sourceStore and only picks up files it has seen in the preprocessor stage.

Now, if you have some other tool that also runs through instrumented code (browserify-istanbul in my case), then the code inside karma-coverage passes in an explicit cache of files. The HTML renderer tries to grab the source file that browserify-istanbul has parsed over, but can't because it's not in the cache that karma-coverage has seen. Long story short, you end up with a Saturday morning spent trying to get both tools to play with each other and that's why this plugin exists.

Specifically, if you end up with a stack like this, then this tool may be useful:

TypeError: Cannot read property 'split' of undefined
    at HtmlReport.Report.mix.writeDetailPage (/Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:412:30)
    at /Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:489:26
    at SyncFileWriter.extend.writeFile (/Users/anil/textio/frontend/node_modules/istanbul/lib/util/file-writer.js:57:9)
    at FileWriter.extend.writeFile (/Users/anil/textio/frontend/node_modules/istanbul/lib/util/file-writer.js:147:23)
    at /Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:488:24
    at Array.forEach (native)
    at HtmlReport.Report.mix.writeFiles (/Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:482:23)
    at /Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:484:22
    at Array.forEach (native)
    at HtmlReport.Report.mix.writeFiles (/Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:482:23)
    at HtmlReport.Report.mix.writeReport (/Users/anil/textio/frontend/node_modules/istanbul/lib/report/html.js:566:14)
    at writeReport (/Users/anil/textio/frontend/node_modules/karma-coverage/lib/reporter.js:62:16)
    at /Users/anil/textio/frontend/node_modules/karma-coverage/lib/reporter.js:290:11
    at /Users/anil/textio/frontend/node_modules/karma/lib/helper.js:82:7
    at FSReqWrap.oncomplete (fs.js:82:15)