Textbox validation with jQuery (required field)

scripts.js

$(document).ready(function () {
  $('#submit').click(function (e) {
  var isValid = true;
    $('#firstname,#lastname,#email,#password').each(function () {
      if ($.trim($(this).val()) == '')
      {
        isValid = false;
        $(this).css({
          "border": "1px solid red",
          "background": "#FFCECE"
        });
      }
      else 
      {
        $(this).css({
          "border": "",
          "background": ""
        });
      }
    });
    if (isValid == false)
      e.preventDefault();
  });
});