Two-pass parsing. The code will be treated as if it was
function f() {
var scope; // var created, but no value assigned. this overrides the earlier global
console.log(scope);
scope = 'local';
console.log(scope);
}
The var's CREATION will be executed as if it was the very first bit of code executed in the function. But the actual assignment operation won't occur until where it normally would.