title: how to get checked radio button value in javascript
body: <p>I have some set of radio button. I am trying to get checked radio button value using java script. But I got the error of uncaught id. I do the following code in html 5. I am not getting the value. </p>
  
  <pre><code>  function timeout()
    {
        if (document.getElementById["RadioButton1"].checked) 
           {
             choice = document.getElementById["RadioButton1"].value;
             alert('choice');
  
           }
  
       if (document.getElementById["RadioButton2"].checked)
          {
            choice = document.getElementById["RadioButton2"].value;
            alert('choice');
          }
       if (document.getElementById["RadioButton3"].checked)
         {
           choice = document.getElementById["RadioButton3"].value;
           alert('choice');
  
        }
      if (document.getElementById["RadioButton4"].checked)
        {
            choice = document.getElementById["RadioButton4"].value;
            alert('choice');
        }
     var c = document.getElementById("label1").value;
  }
  </code></pre>