The difference is that functionOne is defined at run-time, whereas functionTwo is defined at parse-time for a script block. For example:
<script> // Error functionOne(); var functionOne = function() { }; </script> <script> // No error functionTwo(); function functionTwo() { } </script>
from: http://stackoverflow.com/questions/336859/var-functionname-function-vs-function-functionname
var functionName = function() {} vs function functionName() {}
原文：http://www.cnblogs.com/Jim-william/p/4618584.html