purefunction.js

//Global Scope.
var globaldata={user:"xyz",loggedin:false,currentstate:"none"}
var userinput="Current State Info";

/* Impure way of handling login. Changing Global State,
operation is dependent upon global variable 'userinput',
no return value.
*/
var login=(globaldata)=>{
globaldata.loggedin=true;
globaldata.currentstate=userinput;
}

//Pure way of handling login.
var login=(globaldata,userinput)=>{
  var globaldatacopy={...globaldata};
  globaldatacopy.loggedin=true;
  globaldatacopy.currentstate=userinput;
  return globaldatacopy;
}