Using parameters in catalog items is useful in many situations.
- Link in an email that references a previous task 
- Link on a website that references a particular issue 
- Auto-fill values for certain catalog items 
Example
Parameter in a URL to set the category field on a catalog item.
Parameter in the URL
https://instance.service-now.com/sp?id=sc_cat_item&sys_id=3f1dd0320a0a0b99000a53f7604a2ef9&sysparm_category=e15706fc0a0a0aa7007fc21e1ab70c2f&sysparm_inc_category=inquiry
Catalog Client Script
function onLoad() {
	var category = getParameterValue('sysparm_inc_category');
	if (category) 
		
	
}
function getParameterValue(name) {
	name = name.replace(/[[]/, "\\[").replace(/[\]]/, "\\]");
	var regexS = "[\\?&]" + name + "=([^&#]*)";
	var regex = new RegExp(regexS);
	var results = regex.exec(top.location);
	if (results == null) {
		return "";
	} else {
		return unescape(results[1]);
	}
}Navigation by URL
If you are interested in how to pass parameters by url in normal ServiceNow forms, check out this article: