javascript - If not declared, declare the variable? -

the topic might bit cryptic, here's problem (perhaps n00b-thing?):

for site have widget, user can use on site such (for example):

<script type="text/javascript">     var widget_width ="300"; </script> <script src="http://something/a.js" type="text/javascript"></script> 

now, in .js file want check if user have declared widget_width variable. thought might (i want variable empty, "", because server-side validation too):

if(typeof widget_width == 'undefined') {     var widget_width = ""; } 

this didn't work, neither did:

if(!widget_width) {     var widget_width = ""; }  

any ideas on how declare variable when needed way?

remove var. make >

if(typeof widget_width == 'undefined') {     widget_width = ""; }