Checking if a textbox is empty in Javascript

Question

This is my code which was supposed to raise an alert message if the textbox is left empty:

function a(id)
{
    var n=document.getElementById(id         


        

Answer 1

your validation should be occur before your event suppose you are going to submit your form.

anyway if you want this on onchange, so here is code.

function valid(id)
{
    var textVal=document.getElementById(id).value;
    if (!textVal.match(/\S/)) 
    {
        alert("Field is blank");
        return false;
    } 
    else 
    {
        return true;
    }
 }