Javascript declare variable in global scope shorthand

Question

var object = {name: "Murad"};
(function(window){
  var a = b = 10;
})(object)

Why I can access b variable in global scope?

var a = b = 10

is not same thing with?

window.b = 10;
var a = window.b;

Answer 1

You can access variable b because you give a variable name - b, but you do not declare it like var let or const. JS will see that a name is allocated for a variable and it will create the variable automatically in the global scope.