Simple Blog with jQuery and validation

This example is an extenstion of the htmljQueryBlog where we add the validation of the fields in the new entry form.

HTML5 supports two new attributes for validating the input fields:

  • required : this is an HTML attribute that can be added to the input fields to tell the browser that this input field is required for the submission of the form.
  • :invalid : this is a CSS selector that can be used for finding the input fields that have an invalid value

In our case we add the required attribute to the title field

%form(action="/new" method="post")
  %input(type = "text" name="title" id="title" placeholder="Post Title" required)
  %textarea(name="content" rows = "5" placeholder = "Content")
  %input(type = "email" name="email" placeholder = "Email")              
  %button#postEntry(type = "submit") Post

Desktop browsers implement various methods for informing the user about the errors in the form. In the case of mobile browsers, it is up to the developers to decide how to present the errors. Due to the small screen size, it's not trivial to decide how to highlight the invalid fields and explain the errors.

In our example we highlight in blue the fields that are required and in red the fields that are invalid. If the user attempts to submit a form that contain an error we show a small error icon near the fields that are invalid.

This is achieved by a combination of CSS and JS

[required] {
  border-color: #88a;
  -webkit-box-shadow: 0 0 3px rgba(0, 0, 255, .5);
:invalid {
  border-color: #e88;
  -webkit-box-shadow: 0 0 5px rgba(255, 0, 0, .8);
input.invalid {
  background: url(error.png) no-repeat 4px 6px;
  padding-left: 30px;
$(function() {
  $("#postEntry").bind("click", function() {
    if ($(":invalid").length) {
      return false;

You can try this example by starting the server and visiting the page http://localhost:4567 in your browser

ruby server.rb