instrument.md

Producing instrumented source

The nyc instrument command can produce instrumented source files. These files are suitable for client side deployment during end to end testing. You can either pre-instrument your source, or write instrumented source to a stream.

Run nyc instrument --help to display a full list of available command options.

Pre-instrumented source

You can create pre-instrumented source code by running:

nyc instrument <input> [output]

<input> can be any file or directory within the project root directory. The [output] directory is optional and can be located anywhere, if not set the instrumented code will be sent to stdout. For example, nyc instrument . ./output will produce instrumented versions of any source files it finds in . and store them in ./output.

The --delete option will remove the existing output directory before instrumenting.

The --complete-copy option will copy all remaining files from the input directory to the output directory. When using --complete-copy nyc will not copy the contents of a .git folder to the output directory.

Note: --complete-copy will dereference any symlinks during the copy process, this may stop scripts running properly from the output directory.

Streaming instrumentation

nyc instrument will stream instrumented source directly to stdout, that can then be piped to another process. You can use this behaviour to create a server that can instrument files on request. The following example shows streaming instrumentation middleware capable of instrumenting files on request.

app.use((req, res, next) => {
  const myOptions = ""
  const filename = myHelper.getFilename(req)
  const nyc = cp.spawn(`nyc instrument ${myOptions} ${filename}`)
  nyc.stdout.pipe(res)
})