I love javascript

magic.js

//Javascript magic here
//We grab the value from the dom element, split it in terms where every
//term is delimited by a comma, then trim every term, re-combine them 
//together using a comma as separator and then URI encode the whole thing.
var fieldVals = encodeURIComponent(
  this.$('#product_search #field_val').val().split(',').map(function(v){
    return v.trim();
  }).join(',')
);