A function sees whatever variables were around when it was created. Here, get and set were created within the same call to assignAccessors, so they see the same x.

Results

var get, set;
function assignAccessors() {
    var x = 1;
    get = function() { return x; }
    set = function(y) { x = y; }
}
assignAccessors();
log(get());
set(10);
log(get());