Change background color of input text field using JavaScript

How do I change the background color of a input text开发者_运维问答 field using java script? I want to insert it in a form validation function like this:

        function validateForm()
        {
        var x=document.forms["form1"]["username"].value;
        if (x==null || x=="")
          {
   document.forms["form1"]["username"].style.backgroundColor = Black
          }
        }

Also, is there a way to do form validation with php without creating two pages? WHat would you recommend? Using JavaScript or php for validating the user input of a form? I already have a php process form which checks whether the user supplied the correct details like the password etc.

Thank you for any help

---

You are taking the value of the text input. You need to refer to the control itself:

function validateForm()
{
    var ctrl = document.forms["form1"]["username"];
    var x=ctrl.value;
    if (x==null || x=="") {
       ctrl.style.backgroundColor = color;
    }
}