title: how i sum the total of button onclick
body: <p>I have this code:</p>
  
  <pre><code>&lt;table&gt;
      &lt;td&gt; 
          &lt;script type="text/javascript"&gt;
              var click3 = 0;
  
              function onClick3() {
                  click3 += 1;
                  document.getElementById("click3").innerHTML = click3;
              };
          &lt;/script&gt;
  
          &lt;button type="button" onClick="onClick3()"&gt;2&lt;/button&gt;
          &lt;a id="click3"&gt;0&lt;/a&gt;
      &lt;/td&gt;
  
      &lt;td&gt;
          &lt;script type="text/javascript"&gt;
              var click4 = 0;
  
              function onClick4() {
                  click4 += 1;
                  document.getElementById("click4").innerHTML = click4;
              };
          &lt;/script&gt;
  
          &lt;button type="button" onClick="onClick4()"&gt;2&lt;/button&gt;
          &lt;a id="click4"&gt;0&lt;/a&gt;
      &lt;/td&gt;
  &lt;table&gt;
  </code></pre>
  
  <p>How do I calculate the sum of the number of times pressed the two buttons?</p>