gistfile1.js

function hola(){
 var myvar = 'hola';
 console.log('1.' + myvar); //prints '1. hola'
 function mundo(){
  console.log('2.' + myvar); //prints '2. hola'
 }
 mundo();
}
hola()
// throws an error:  Uncaught ReferenceError: myvar is not defined 
// because myvar it's only available within hola function
console.log('3.' + myvar);