Jerb is a project mainly written in JavaScript, it's free.
ERB for JavaScript
watch
new JERB('hello <% name %>').render({name:'Steve'});
//-> 'hello Steve'
new JERB('hello <% name %>').save('greeting');
JERB.render('greeting', {name:'Jared'});
//-> 'hello Jared'
new JERB('<%= render('greeting') %>,
Welcome to <%= service_name %>!').save('welcome letter');
JERB.render('welcome letter', {name:'Paul', service_name:'HitGub'})
//-> 'hello Paul, Welcome to HitGub!
see example.html