In addition to the Peter's Solution,
If the string is in the format which you have provided, then you shall try this to convert it to a json object.
var params = "domain:Abcd-E-Group,domaintype:com,Submit1:Search";
var jsonStrig = '[{';
var items = params.split(',');
for (var i = 0; i < items.length; i++) {
var current = items[i].split(':');
jsonStrig += '"' + current[0] + '":"' + current[1] + '",';
}
jsonStrig = jsonStrig.substr(0, jsonStrig.length - 1);
jsonStrig += '}]';
alert(jsonStrig);
var obj = JSON.parse(jsonStrig);
alert(obj[0].domain);