How to check whether a TextBox has value or not using JavaScript

Using JavaScript we can perform client side validation. It will improve the performance of your web application. Here i have shown a simple basic validation, how to check whether a text box has value or not.

    var username=document.getElementById("uname").value;  
    if (username==null || username=="")  
    {  
        alert("Please Enter Username");  
        document.getElementById("uname").focus();  
    }  

Here the alert is used to display a message box with the text it has. And the focus() is used to move the cursor to the corresponding text box.