title: checked first radio button as default using javascript only
body: <pre><code>&lt;input id="a" type="radio" name="radioButton"&gt;
  &lt;input id="b" type="radio" name="radioButton"&gt;
  &lt;input id="c" type="radio" name="radioButton"&gt;
  &lt;input id="d" type="radio" name="radioButton"&gt;
  </code></pre>
  
  <p>Lets say I have four radio buttons and how do I make the <code>first-child</code> to be <code>checked</code> as default by using just javascript, no jQuery please.</p>
  
  <p>This is what I have done but did not work. Thanks in advance.</p>
  
  <pre><code>document.querySelectorAll('[name=radioButon]:first-child').checked = true; 
  </code></pre>