console.log(foo); // ReferenceError: foo is not defined
foo =1 ;


console.log(foo); // output is undefined because var declaration bubbles into the top of the file .Hoisting
var foo =1 ;


console.log(foo); // ReferenceError: foo is not defined .
let foo =1 ;


foo =3 ;
console.log(foo);
var foo ; 
// output should be 3 because the var declaration of foo is now bubbled at the top so we can think that var foo exists even before foo=3 is declared



// bubbles to the top
foo(); // no errors
function foo(){

}