[SalesForce] Access url parameter from lightning component Lightning

I have a url link on a lightning component on customer community. When I click the link, I redirect to other lightning component.

<aura:attribute name="Url1" type="String" default="./commonClass?par=True?id=" description="URL to the common page." />
<li class="slds-item"><a href="{!v.Url1}">commonpage1</a></li>

Now, I would like to access the parameter "par" from the url link on new lightning component after redirecting. How can i do it?
I went through Getting the URL parameter into Lightning component using the "{! paramName}" expression and Lightning App – getting URL parameter, but I dont see any <aura:application/> to declare my attribute there.

Updated:
cmp:

 <aura:attribute name="int" type="String" description="Boolean from url to show Intermittent Report." />

controller.js:

doInit : function(component, event, helper) {

        helper.getParameterByName(cmp,event,'int');
    }

helperjs:

getParameterByName : function(cmp,event,name) {
   url = window.location.href;
   name = name.replace(/[\[\]]/g, "\\$&");
   var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)"),
   results = regex.exec(url);
   if (!results) return null;
   if (!results[2]) return '';
   //return decodeURIComponent(results[2].replace(/\+/g, " "));
        component.set('v.int', decodeURIComponent(results[2].replace(/\+/g, " ")));

},

It says, WARNING: Callback failed: in inspect element chrome.

Please guide.

Thank you

Best Answer

This is a limitation, you cannot access the URL parameters in lightning components via an expression tag .

If the hashed part of the URL is changing then there is a neat event to handle and you can read what has changed

aura:locationChange event

If your URL hash is not changing then you can use javascript to do this in your controller.js using below code

doInit: function(component, event, helper) {
  // This is url query parameter
  var value = helper.getParameterByName(component , event, 'variable');
  // Set the value, assumes you have created attribute "attributename" in your markup
  component.set("attributename", value);
}

and your helper.js will have a common function to read URL parameter

getParameterByName: function(component, event, name) {
  name = name.replace(/[\[\]]/g, "\\$&");
  var url = window.location.href;
  var regex = new RegExp("[?&]" + name + "(=([^&#]*)|&|#|$)");
  var results = regex.exec(url);
  if (!results) return null;
  if (!results[2]) return '';
  return decodeURIComponent(results[2].replace(/\+/g, " "));
}
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