html loading introduced with the execution order and js

1. Because js is an interpreted language, so the translation is progressive, so the line of code is interpreted contained in the reference object (such as: Style), etc. must be in before the trip.
2. Code $ (function () {}) it is performed only when the page will be loaded.
3. $ () On (event, target, function);. This target is triggered only when the event will be interpreted so do not worry about the undefine.