Javascript CSOM - Add SP Group to a SP Site with broken inheritance

I have a SP Sub-site with broken inheritance.

Using Javascript and SharePoint Client Side API, I want to add an existing SP Group from Site-Collection to the sub-site with full-control permission level access.

Can anyone help how can I do this?

I have tried some sample code,  code is running with no errors  but it is not adding that group to the subsite, any help would be appreciated.

Below is my code:

function createSPGroup()
	{
	    //Load new Site
	    var currentCTX = new SP.ClientContext();
	    var currentWEB  = currentCTX.get_web('/subsiteUrl');

	    //Get all groups in site
	    var groupCollection = currentWEB.get_siteGroups();

	    // my group
   	    var leadershipGRP = currentWEB.get_siteGroups().getByName("Group Name");

     	   var rdFullControl = currentWEB.get_roleDefinitions().getByName('Full Control');

	  // Create a new RoleDefinitionBindingCollection.
          var collFullControl  = SP.RoleDefinitionBindingCollection.newObject(currentCTX);

         // Add the role to the collection.
         collFullControl.add(rdFullControl);

	// Get the RoleAssignmentCollection for the target web.
        var assignments = currentWEB.get_roleAssignments();

        // assign the group to the new RoleDefinitionBindingCollection.
        var roleAssignmentLeadership = assignments.add(leadershipGRP, collFullControl);

	currentWEB.update();
	currentCTX.load(leadershipGRP);
	currentCTX.load(roleAssignmentLeadership);

	currentCTX.executeQueryAsync(Function.createDelegate(this, success), Function.createDelegate(this, this.failed));
}

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