title: The property 'value' does not exist on value of type 'HTMLElement'
body: <p>I am playing around with typescript and am trying to create a script that will update a p-element as text is inputted in a input box.</p>
  
  <p>The html looks as following:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;html&gt;
      &lt;head&gt;
      &lt;/head&gt;
      &lt;body&gt;
          &lt;p id="greet"&gt;&lt;/p&gt;
          &lt;form&gt;
              &lt;input id="name" type="text" name="name" value="" onkeyup="greet('name')" /&gt;
          &lt;/form&gt;
      &lt;/body&gt;
      &lt;script src="greeter.js"&gt;&lt;/script&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>And the <code>greeter.ts</code> file:</p>
  
  <pre><code>function greeter(person)
  {
      return "Hello, " + person;
  }
  
  function greet(elementId)
  {
      var inputValue = document.getElementById(elementId).value;
  
      if (inputValue.trim() == "")
          inputValue = "World";
  
      document.getElementById("greet").innerText = greeter(inputValue);
  }
  </code></pre>
  
  <p>When I compile with <code>tsc</code> I get the following "error":</p>
  
  <p><code>/home/bjarkef/sandbox/greeter.ts(8,53): The property 'value' does not exist on value of type 'HTMLElement'</code></p>
  
  <p>However the compiler does output a javascript file, which works just fine in chrome.</p>
  
  <p><strong>How come I get this error? And how can I fix it?</strong></p>
  
  <p>Also, where can I look up which properties are valid on a <code>'HTMLElement'</code> according to typescript?</p>
  
  <p>Please note I am very new to javascript and typescript, so I might be missing something obvious. :)</p>