How to read Liferay's URL parameter via script

Steps to read Liferay URL parameter via script.

1) Add a tag in your .JSP to read portlet namespace
<%@ taglib uri="http://java.sun.com/portlet_2_0" prefix="portlet" %>

2) Create a global script variable inside your JSP for portlet name space
<script type="text/javascript" charset="utf-8">
var portletNamespace ='<portlet:namespace/>';
</script>

In a js file we can not use '<portlet:namespace/>' directly, hence we need to create a global js variable which can be accessed in .js file.

3) Create a function which reads and returns the URL parameter
function getURLParameterValue(parameterName, url) {
parameterName = parameterName.replace(/[\[]/, '\\\[').replace(/[\]]/, '\\\]');
var results = new RegExp('[\\?&]'+parameterName+'=?([^&#]*)').exec(url || window.location.href);
return results == null ? null : results[1];
}

Here, function accepts two values
#1) "parameterName" whose value needs to be read (This is an actual name from the URL parameter)
#2) "url" (Its an href location / window's current URL)

4) Read the URL in the javascript function
Let's say this is your URL :     <protocol>://<hostname>:<port>/group/control_panel/manage?p_auth=asdfg&p_p_auth=xyz&p_p_id=_sometext_WAR_sometextportlet_&p_p_lifecycle=1&p_p_state=maximized&p_p_mode=view&doAsGroupId=12345&refererPlid=5555&_sometext_WAR_sometextportlet_id=123456

Ex: Read Liferay Parameter
>) getURLParameterValue(portletNamespace + "id", window.location.href)
will return "123456"
Ex: Read Any parameter without portletNamespace prefixed
>) getURLParameterValue("p_auth", window.location.href) 
will return "asdfg"

Cheers!
Henal Saraiya
(Senior Consultant)
CIGNEX Datamatics