A small problem with js closures

The following two sections of code functiona () {varb1; window. setTimeout (function () {// when a timer is used to trigger the call, alert (B) ;}, 3000 );... syntaxHighlighter. all (); the following two sections of code

Function a () {var B = 1; window. setTimeout (function () {// If a timer is used to trigger the call, alert (B) ;}, 3000) ;}a ();

 

Function a () {var B = 1; window. setTimeout (function () {// If a timer is used to trigger the trigger, alert (B); var B = 2 ;}, 3000) ;}a ();

 

What is the execution result if there is only one sentence missing? First, smooth pop-up. Second, undefined. How can I understand it? Js initializes the variable defined by var, causing the variable B in the second to initialize the local variable, which means that B has been released.