title: What is difference between ClientID and document.getElementById()?
body: <p>I have a asp.net text box and I get Id of text box using  </p>
  
  <pre><code>var tbFilterValueClientID = "&lt;%= tbFilterValue.ClientID %&gt;";
  </code></pre>
  
  <p>But when I am using it so I do</p>
  
  <pre><code>var tbFilterValue = document.getElementById(tbFilterValueClientID);
  </code></pre>
  
  <p>After that I am able to perform and get value of it like:</p>
  
  <pre><code>var filterValue = tbFilterValue.value.toString().trim();
  </code></pre>
  
  <p>So can anyone explain why I need to </p>
  
  <blockquote>
    <p>document.getElementById</p>
  </blockquote>
  
  <p>and Pass Id of control? Why can I not use </p>
  
  <blockquote>
    <p>tbFilterValueClientID</p>
  </blockquote>
  
  <p>directly?</p>