remove non alphanumeric chars + output last 6 chars

[ZxIRAX]

I am looking for some help creating a script, ideally in JS if this is possible.

Essentially the end user will paste a string of characters (varying in length anything from 11-18 characters) into a text box, then click a button which will remove any non alphanumeric characters and spaces and display the last 6 digits of the string.

For example, the user pastes: 7/9684798- 3
The output should be: 847983

Any help would be great!

[vwphillips]

var N='7/9684798- 3';
N=N.replace(/\D/g,'');
alert(N.substring(N.length-6));