[Deff]

<script type="text/javascript">
function cb1 (){
  alert('this')
} cb1()
</script>

<script type="text/javascript">
cb1 = function (){
  alert('this')
} cb1()
</script>

<script type="text/javascript">
cb1 = function (){
  alert('this')
} 
cb1()
</script>