trying to understand the difference between window and document objects in js [duplicate]

Answer 1

JavaScript that runs in the browser has Window as it's top level. This means that global variables will become properties of window:

// this code is not inside a function
var global1=22;
function test(){
  var local=88;
  window.global2=99;
  console.log(local);//logs 88 because
    // local is available within the body
    // of this function
  console.log(global1);//logs 22
}
console.log(typeof local);//logs undefined becaue were
  // outside the funciton body
test();
console.log(global2);//logs 99 because we added
   // global2 as a property of window

So window will contain all your global objects, this means that: parseInt does the same as window.parseInt.

Window even contains itself so:

window===window.window.window;//is true

window does not have a getElementById, children, childNodes ... funciton because window is not an Html element and document is.