node.js - Handling saves and redirects asynchronously in node js and mongoose -

i new node.js , trying understand asynchronous nature of how stuff works. ok simple form submission.the model looks below:-

var mongoose=require('mongoose'); var schema=mongoose.schema; var postschema=new schema({ title:{type:string,required:true},     post:string, }); var postmodel=mongoose.model('blogpost',postschema); module.exports=postmodel; 

and route handler below:-

app.post("/submitpost",function(req,res){         var title=req.body.title;         var post=req.body.post;         var thepost=new postmodel({title:title,post:post});         thepost.save(function(err,data){             if(err)throw err;             console.log(data);         })     console.log("title "+title);     console.log("post "+post);     res.send("saved");   }); 

now suppose validation fails during "thepost.save(callback)" , want show error page rather "saved" . how that?

simply move rendering of response callback:

app.post("/submitpost",function(req,res){         var title=req.body.title;         var post=req.body.post;         var thepost=new postmodel({title:title,post:post});         thepost.save(function(err,data){             if(err) {               res.render('errorpage');             } else {               console.log(data);               console.log("title "+title);               console.log("post "+post);               res.send("saved");             }         })   });