title: button for zoom in three.js
body: <p>I use three.js and THREE.OrbitControls for animation
  I dont know how change zoom with button click
  How I understand ..for zooming  answer this functions</p>
  
  <pre><code>this.dollyIn = function ( dollyScale ) {
          if ( dollyScale === undefined ) {
              dollyScale = getZoomScale();
          }
          scale /= dollyScale;
  
      };
  
      this.dollyOut = function ( dollyScale ) {
          if ( dollyScale === undefined ) {
              dollyScale = getZoomScale();
          }
          scale *= dollyScale;
  
      };
  </code></pre>
  
  <p>what I need send to increment or decrement zoom
  I how do it for this button form ??</p>
  
  <pre><code>&lt;input id="clickMe" type="button" value="+" onclick="..." /&gt; 
  </code></pre>