javascript - Check for a GET variable in URL -

so i'm making simple log in form in site using jade , expressjs. it's working, problem i'm having when user enters incorrect log in details. when enter wrong details redirect them log in page parameter in url (/admin?falselogin). question is: how can check if variable exists in jade view?

this code:

log-in.jade

form(action="/log-in" method="post")     label username     input(type="text" class="form-control" name="username" placeholder="username")     label password     input(type="text" class="form-control" name="password" placeholder="password")     input(type="submit" class="btn btn-info pull-right" style="margin-top: 15px;" value="log in") 

app.js

app.get("/admin",function(req, res){      if(req.session.username){         res.render("admin", {session_name: req.session.username});     }else{         res.render("log-in");     }  });  app.post("/log-in", function(req, res){      var admin = admin.findone({"username": req.body.username, "password": req.body.password});     admin.count(function(error, count){         //console.log(count);         if(count > 0){             req.session.username = req.body.username;             res.redirect("/admin");         }else{             res.redirect("/admin?falselogin");         }     }); }); 

i tried following inside jade view error cannot read property 'location' of undefined:

- var page = window.location.pathname  if page === "/admin?falselogin"     .alert.alert-danger error! wrong details, please try again! 

i come php background, in php able check directly in html using:

<?php if(isset($_get['falselogin'])){// display error user } ?> 

any appreciated. thanks!

first, recommend using full key-values query string, /admin?login=false

then use req.query specific variable , pass jade view or using res.locals make variable accessible in views.

app.js

app.get("/admin",function(req, res){    res.locals.login = req.query.login; // accessible in view 'login'    if (req.session.username) {     res.render("admin", {session_name: req.session.username});   } else {     res.render("log-in", {       login: req.query.login, // or pass variable view directly, accessible in view 'login'     });   } }); 

reasoning. don't think it's practice parse url query directly in view. while fine raw php example using $_get, if use mvc framework, laravel example, move away that. let controller job of handling logic based on queries , handing off relevant information views. in view, should simple presentation logic.