internal/modules/cjs/loader.js:638 throw err

I was created angular project and try to connect mongodb database using db.js file.and also i am getting error: Cannot find module. what should i do ? please help me

internal/modules/cjs/loader.js:638
throw err;
^

Error: Cannot find module 'C:\Users\user\Desktop\angularproject\db.js'
at Function.Module._resolveFilename (internal/modules/cjs/loader.js:636:15)  
at Function.Module._load (internal/modules/cjs/loader.js:562:25)
at Function.Module.runMain (internal/modules/cjs/loader.js:831:12)
at startup (internal/bootstrap/node.js:283:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:622:3)

My db.js file contains following code

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/CrudDB',(err) => {
if(!err)
console.log('MongoDB connection succeed.');
else
console.log('Error in DB connection:'+ JSON.stringify(err,undefined,2));
});

module.exports = mongoose;