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 --in-place option will allow you to run the instrument command.

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 <input> will stream instrumented source directly to stdout and that output can then be piped to another process. You can use this behaviour to create a server that dynamically instruments 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)
})