How to Enable Or Disable Submit Button Using Jquery
We can disable or enable any form element like button using Jquery prop or attr.
If Jquery version is 1.6 or above, we can use Jquery prop.
If Jquery version is 1.5 and below, we can use Jquery attr.
Lets consider one example here.
Suppose we have a TextBox and Button as shown below.

Initially, when there is nothing on the textbox, the Button will be disabled.

When we type anything on the textbox, the button should be enabled.

So on the KeyUp event of Textbox, we can apply following logic in Jquery.
$(function () {
    $('#btnInput').prop('disabled', true);
    $('#txtInput').keyup(function () {
        if ($(this).val() != '') {
            $('#btnInput').prop('disabled', false);
         }
    });
})
If Jquery version is 1.5 and below, we can use Jquery attr.
$(function () {
    $('#btnInput').attr('disabled', 'disabled');
    $('#txtInput').keyup(function () {
        if ($(this).val() != '') {
            $('#btnInput').removeAttr('disabled');
         }
    });
})