JavaScript Variable initialization location

The variable is initialized in the previous <script type= "Text/javascript" ></script> (or the referenced JS file) and can be accessed normally.

Run the program: Eject 123.

<script type= "Text/javascript" > var a = 123; </script><script type= "Text/javascript" > alert (a); </script>

Variables are initialized in the <script type= "Text/javascript" ></script>, the variables are initialized in the code after they are accessed, and the variables are not accessed (defined but not valued).

Run the program: Eject undefined.

<script type= "Text/javascript" > alert (a);
　　var a = 123;
</script>

The variable is initialized in subsequent <script type= "Text/javascript" ></script>> (or the referenced JS file) and is not accessible (equivalent to undefined).

Run Program: Error, hint A is undefined.

<script type= "Text/javascript" > alert (a); </script><script type= "Text/javascript" > var a = 123;
</script>

JavaScript Variable initialization location