javascript - Jquery $(this).val(); on .ready not working -

I'm trying to get the value of the option of a dropdown (the selection is an ID on the markup), while opening the web Page

Using

  $ (document) .ready (function () {$ ('# cat_list'). Ready (function () {var category = $ (This) .val (); Alert (category);});});   
 I get an empty alert.  
 But. (When selecting something else inside the dropdown) The following code works perfectly with the same task  
  $ (document) .ready (function () {$ ('# Cat_list '). Change (function () {var category = $ (this) .val (); Alert (category);});}); Finally, it works using the original javascript and it can successfully, open, refresh value, fail on the form ... etc.  
  $ (document) .ready (function () {$ ('# cat_list') ready (function () {var e = document.getElementById ("cat_list"); var category = e.options [e.selectedIndex] .value; Alert (class);});});   
 Thanks for any help why the first version .ready + $ (this) .val (); Unsuccessful   
 
 
 The correct code is:  
  $ (document) .ready (Function () {var class = $ ('# cat_list'). Val (); Alert (category);});