如何在HTML文本框中检查null值？

Question

I have a JSP page where i am fetching value from html textbox.
I want to insert that value into MySQL database. I want if textbox in empty,null,zero and undefined then insert 0 in database otherwise actual value insert in database.

Here is my code.

Strins s1=request.getparameter("edate");
s1="1990-07-16 09:12:45"
int s4=0

<script>
    var a=<%=s1%>
    if(a==null || a==undefined || a=='' || a==0){                
       <% psmnt.setInt(6,s4); %>
    }
    else{
       <% psmnt.setString(6,s1); %>
    }
</script>

Answer 1

You can use this

<script>
if(typeof a == 'undefined' || a == 0) {
// Insert db 0
}
</script>

Answer 2

Is your texbox <texarea> or <input type="text"> ?

If you are using <input type="text"> , put default value on it:

 <input type="text" value="">

While for <textarea> , <textarea></textarea> should give your default value ""

So that you only need to check

if(a==''){
    ......
}

Or if you didn't allow white space too, do this:

if(a=='' || a.trim() ==''){
    ......
}