node.js - Bcrypt error: illegal arguments String unidentified -

here complete code

var express = require('express'),     app = express(),     mongoose = require('mongoose'),     bodyparser = require('body-parser'),     morgan = require('morgan'),     webtoken = require('jsonwebtoken'),     bcrypt = require('bcryptjs'),     assert = require('assert');     schema = mongoose.schema,     secretkey = "omjdiuwkslxmshsoepdukslsj";  //user schema var userschema = new schema({     username: {type: string, required: true, index: {unique:true}},     password: {type: string, required: true, select: false} })  userschema.pre('save', function(next){     var user = this;      if(!user.ismodified('password')) return next();      bcrypt.hash(user.password, null, null, function(err, hash){         if(err) return next(err);          user.password = hash;         next();     }) });  userschema.methods.comparepassword = function(password){     var user = this;      bcrypt.compare(password, user.password, function(err, result){         if(err){             console.log(err);         }         else {             console.log("passwords match!");             return;         }     }) }  var usermodel = mongoose.model('users', userschema);   //connecting mongo mongoose.connect("mongodb://localhost/userstories", function(err){     if(err) {         console.log(err);     }     else {         console.log("connected database!");     } });  //creating token function createtoken(user){     var token = webtoken.sign({         _id: user.id,         username: user.username     },  secretkey,{         expiresin: 30 * 60 * 1000     })     return token;     }  //middlewares app.use(bodyparser.urlencoded({extended: true})); app.use(bodyparser.json()); app.use(morgan('dev'));  //api's  app.post('/signup', function(req, res){         var user = new usermodel({         username: req.body.username,         password: req.body.password     })      user.save(function(err){         if(err){             console.log(err);         }          else{             res.json({message: "user created!"});         }     }) })  app.post('/login', function(req, res){      usermodel.findone({username: req.body.username}, function(err, user){         if(err) console.log(err);              if(!user){                 res.send("user not found!");             }                  else if(user){                        var validpassword = user.comparepassword(req.body.password);                         if(validpassword){                                 var tokens = createtoken(user);                                  res.json({                                     success: true,                                     message: "successfully logged in",                                     token: tokens                                 });                         }                               else {                                     res.send("invalid password");                                   }                       }     }) });   //running server app.listen(3000, function(err){     if(err) console.log("port not working");     else{         console.log("everything went fine");     } }) 

i've tried every approaches , saw answers here. no 1 seem come across illegal argument error. please figure 1 out me im sure there bug cant see

i encountered same error when using bcrypt.comparesync("input compared hash", hash).

later on discovered supposed pass actual value in first input parameter i.e (the actual value hash generated) , hash in second input parameter, passing hashed values in both input parameters.

after correcting same giving me desired output true or false.

you can run , check code here.