What is the difference between non-initialized items in an array in JavaScript vs Java?

Question

I was just playing around with JavaScript and got stuck with a simple program.

I declared an array in JavaScript like

var a = [0, 1, 2];

Answer 1

An array is a continuous collection of data. Say if you have a value at index 1 and index 10, the rest will be filled by undefined.

You can't create an array with empty values. 'Empty in your sense', is not undefined or null, it's empty :)

That continuous data is undefined means default assignment in JavaScript.

Say if you defined a variable,

var X;
console.log(X)    //Undefined

it's not null. null is a user explicitly specifying a way to tell there is an empty data, and undefined is the JavaScript engine way.