Intercept a form submit in JavaScript and prevent normal submission

There seems to be lots of info on how to submit a form using javascript, but I am looking for a solution to capture when a form has been submitted and intercept it in javascript.

HTML

<form>
 <input type="text" name="in" value="some data" />
 <button type="submit">Go</button>
</form>

When a user presses the submit button, I do not want the form to be submitted, but instead I would like a JavaScript function to be called.

function captureForm() {
 // do some stuff with the values in the form
 // stop form from being submitted
}

A quick hack would be to add an onclick function to the button but I do not like this solution... there are many ways to submit a form... e.g. pressing return while on an input, which this does not account for.

Ty