why if statement isn't looking for a variable in global scope

Question

I am trying to understand scoping in JS.Here i have an example which has a variable in global scope called check.It has a truthy value i mean 1.Then inside a function called main which doesn't have a variable called check but has an if statement which checks whether there is a check variable or not ,upon which it reassign another value to check variable.Then prints it out.if i use

if(check){}

it prints undefined.Here i have some questions:

1. check variable is declared in global scope.It means it has access everywhere.Then even if the IF statement fails it should print the globally assigned value which is 1 instead of undefined.Why it prints undefined instead of 1??

2. main function scope doesn't have a check variable.When if fails to find check inside main function's scope ,why it doesn't look for it in global scope??

  (function(){
        var check=1;
        function main(){
		    if(check){
               var check=10;
	        }
			document.write(check);
			}
		main();
    })();

Answer 1

JavaScript only has function scope and something called hoisting. Every variable declaration inside a function gets put at the beginning of the function. Thus, your code is equivalent to

var check=1;
function main(){
  var check; // = undefined
  if(check){ // block doesn't create scope
    check=10;
  }
  document.write(check);
}

The local variable check shadows the outer variable check.