How do I use yyyy-mm-dd format in javascript?

I'm a beginner at javascript. I need to figure out how to convert my date to be yyyy-mm-dd format and not the "dateformat" "yyyy/mm/dd" i'm getting now. "+DayOfMonth+" which = mm/dd/yyyy

Thanks,

B

<script language="JavaScript">
<!--
 
// function to populate the date on the form and to close this window. --->
function ShowDate(DayOfMonth) {
    var FormName="<cfoutput>#URL.FormName#</cfoutput>";
    var FieldName="<cfoutput>#URL.FieldName#</cfoutput>";
    eval("self.opener.document." + FormName + "." + FieldName + ".value='"+DayOfMonth+"'");
    window.close();
}
 
//-->
</script>

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