Issue while trying to append route parameter in js

Below is my js code that is appending the route and its parameter in anchor tag.

var href = "{!! route('ShowUserMainForm', ['RoleID'=>" + row.RoleID + "]) !!}";

var UserColumn = "<td><a href=' " + href + "'><button>Users</button></a></td>";

It gives below url

http://localhost:1234/public/system-users/%20+%20row.RoleID%20+%20

I am expecting below.

http://localhost:1234/public/system-users/1

Am I missing anything?