title: Unable to set data attribute using jQuery Data() API
body: <p>I've got the following field on an MVC view:</p>
  
  <pre><code>@Html.TextBoxFor(model =&gt; model.Course.Title, new { data_helptext = "Old Text" })&lt;/span&gt;
  </code></pre>
  
  <p>In a seperate js file, I want to set the <code>data-helptext</code> attribute to a string value. Here's my code:</p>
  
  <pre><code>alert($(targetField).data("helptext"));
  
  $(targetField).data("helptext", "Testing 123");
  </code></pre>
  
  <p>The <code>alert()</code> call works fine, it shows the text "Old Text" in an alert dialog. However, the call to set the <code>data-helptext</code> attribute to "Testing 123" does not work. "Old Text" is still the attribute's current value.</p>
  
  <p>Am I using the call to data() incorrectly? I've looked this up on the web, and I can't see what I'm doing wrong.</p>
  
  <p>Here's the HTML markup:</p>
  
  <pre><code>&lt;input data-helptext="Old Text" id="Course_Title" name="Course.Title" type="text" value="" /&gt;
  </code></pre>