Fixed doctest problems.

lib/scatter.js

@@ -865,10 +865,11 @@ export class DOMScatterContainer {
      * @param {String} [touchAction=none] - CSS to set touch action style, needed to prevent
      *                              pointer cancel events. Use null if the
      *                              the touch action should not be set.
+     * @param {DOM node} debugCanvas - Shows debug infos about touches if not null
      */
     constructor(
         element,
-        { stopEvents = 'auto', claimEvents = true, useCapture = true, touchAction = 'none' } = {}
+        { stopEvents = 'auto', claimEvents = true, useCapture = true, touchAction = 'none', debugCanvas = null } = {}
     ) {
         this.onCapture = null
         this.element = element
@@ -900,7 +901,7 @@ export class DOMScatterContainer {
             mouseWheelElement: window
         })
 
-        if (typeof debugCanvas !== 'undefined') {
+        if (debugCanvas !== null) {
             requestAnimationFrame(dt => {
                 this.showTouches(dt, debugCanvas)
             })