Read from serialize to populate form

Check out http://phpjs.org/functions/unserialize:571

I recommend instead of serializing data for communication with javascript, you use JSON. PHP should have json_encode() and json_decode() to help with this, and javascript also has built in JSON handling functions, which you may not even need. For example, if $.getJSON gets a valid JSON string from the server, it will be transformed into a javascript object automatically.

EDIT: assuming you are talking about jQuery's $.serialize(), that I know of there's no function to undo this (I'm not even sure why that would ever be necessary..) but this should work:

$.each(serialized.split('&'), function (index, elem) {
   var vals = elem.split('=');
   $("[name='" + vals[0] + "']").val(vals[1]);
});

Here is the updated version of Explosion Pills' answer with the additional suggestions in the comments applied:

$.each(serialized.split('&'), function (index, elem) {
   var vals = elem.split('=');
   $("[name='" + vals[0] + "']").val(decodeURIComponent(vals[1].replace(/\+/g, ' ')));
});