gistfile1.txt

// What you have

x = 1;
function foo() {
  x = 2;
}
foo();
return x; // Gives 1

// What he wants
x = 1
function foo() {
  x = 2;
}
foo();
return x; // Gives 2

// Also what he wants (meaning of "doesn't leak"):
function foo() {
  x = 2;
}
foo();
return x; // Error - first definition of 'x' doesn't leak into outer scope