title: how to set HTML attribute values in runtime using javaScript?
body: <p>I want to make a theme Switcher.</p>
  
  <p>My idea is to make a div class with many anchor elements (the themes) containing a <code>data-theme</code> attribute which contains different swatches (<code>a</code>,<code>b</code>,<code>c</code>,<code>d</code>,<code>e</code>). I want to replace the <code>data-theme</code> attribute of every page with the <code>data-theme</code> selected when the user clicks a link. How can I make that using JavaScript? </p>