learnyounode/exercises/filtered_ls/problem.md

Learn You The Node.js For Much Win! An intro to Node.js via a set of self-guided workshops.

Create a program that prints a list of files in a given directory, filtered by the extension of the files. You will be provided a directory name as the first argument to your program (e.g. '/path/to/dir/') and a file extension to filter by as the second argument.

For example, if you get 'txt' as the second argument then you will need to filter the list to only files that **end with .txt**. Note that the second argument _will not_ come prefixed with a '.'.

Keep in mind that the first arguments of your program are not the first values of the `process.argv` array, as the first two values are reserved for system info by Node.

The list of files should be printed to the console, one file per line. You **must** use asynchronous I/O.

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## HINTS

The `fs.readdir()` method takes a pathname as its first argument and a callback as its second. The callback signature is:

```js
function callback (err, list) { /* ... */ }
```

where `list` is an array of filename strings.

Documentation on the `fs` module can be found by pointing your browser here:
  {rootdir:/docs-nodejs/fs.html}

You may also find node's `path` module helpful, particularly the `extname` method.

Documentation on the `path` module can be found by pointing your browser here:
  {rootdir:/docs-nodejs/path.html}