Protect online forms from spam by making them perform Proof of Work (PoW).

Place hashcasher.js, sha3.js, and worker.js in the highest-level directory that you wish to be protected by hashash. This is important, because the worker process (which handles the heavy load of crypto, away from the UI thread) can only be used when it is at or above your current depth in the tree.

Add to the page of the form which you'd like to protect:

<script src="/hashcasher.js"></script>

Change your <form> element to have the require property set to hashcash:

<form method="POST" action="/some-endpoint" require="hashcash">
  ...
</form>

The form's submit handler will be used to consume the form's data (its <input> values), pass them to worker.js to compute the proof of work, then submit the form with an attached X-Hashcash header.

Hashcasher comes with a Connect-style middleware, for use in applications built with things like Express. Using it is simple:

// specify the difficulty as "2"
var hashcash = require('hashcasher')(2);

app.post('/some-endpoint', hashcash, ...);

npm install -g http-server and http-server ., then visit localhost:8080/test.html.