ES5 has a lot of interesting hoisting bugs. For example this doesn't print what you expect: for (var i = 0; i < 3; i++) { var text = 'number ' + i;

ES5 has a lot of interesting hoisting bugs. For example this doesn't print what you expect: for (var i = 0; i < 3; i++) { var text = 'number ' + i; setTimeout(function() { console.log(text); }, i * 1000); } But flipping var to let will fix it. The bug is that var is not block-scoped so everything refers to the same `text` variable which gets mutated by the next iteration. I was hoping their demo would be good for explaining this bug but it seems to be broken.