diff --git a/js/NumberSpinner.js b/js/NumberSpinner.js
index eefcdbb9..07bd330e 100644
--- a/js/NumberSpinner.js
+++ b/js/NumberSpinner.js
@@ -9,7 +9,6 @@
 
 import Property from '../../axon/js/Property.js';
 import Utils from '../../dot/js/Utils.js';
-import inherit from '../../phet-core/js/inherit.js';
 import merge from '../../phet-core/js/merge.js';
 import StringUtils from '../../phetcommon/js/util/StringUtils.js';
 import PhetFont from '../../scenery-phet/js/PhetFont.js';
@@ -33,121 +32,120 @@ const ARROWS_POSITION_VALUES = [
 // possible values for options.valueAlign
 const VALUE_ALIGN_VALUES = [ 'center', 'left', 'right' ];
 
-/**
- * @param {Property.<number>} numberProperty value, must be an integer
- * @param {Property.<Range>} rangeProperty - Dynamic range of values, min and max must be integers
- * @param {Object} [options]
- * @mixes AccessibleNumberSpinner
- * @constructor
- */
-function NumberSpinner( numberProperty, rangeProperty, options ) {
-
-  assert && assert( rangeProperty.value.contains( numberProperty.get() ),
-    'value ' + numberProperty.get() + ' is out of range ' + rangeProperty.value.toString() );
-
-  options = merge( {
-    enabledProperty: new Property( true ),
-
-    // {string} where to place the arrow buttons, see ARROWS_POSITION_VALUES
-    arrowsPosition: 'bothRight',
-
-    // {number|null} By default, arrows are scaled to fit dimensions of value background. This is an additional scale factor.
-    arrowsScale: null,
-    arrowButtonFill: 'white',
-    arrowButtonStroke: 'black',
-    arrowButtonLineWidth: 1,
-
-    // {function|null} function called when the increment button is pressed, defaults to adding options.deltaValue
-    incrementFunction: null,
-
-    // {function|null} function called when the decrement button is pressed, defaults to subtracting options.deltaValue
-    decrementFunction: null,
-
-    valuePattern: SunConstants.VALUE_NAMED_PLACEHOLDER, // {string} must contain SunConstants.VALUE_NAMED_PLACEHOLDER
-    decimalPlaces: 0,
-    deltaValue: 1, // may be ignored if incrementFunction and decrementFunction are provided
-    font: new PhetFont( 28 ),
-
-    // {string} alignment for value, see VALUE_ALIGN_VALUES
-    valueAlign: 'center',
-    xSpacing: 5,
-    ySpacing: 3,
-
-    // background node
-    xMargin: 5,
-    yMargin: 3,
-    cornerRadius: 5,
-    backgroundMinWidth: 0,
-    backgroundFill: 'white',
-    backgroundStroke: 'black',
-    backgroundLineWidth: 1,
-
-    // arrow button pointer areas
-    touchAreaXDilation: 0,
-    touchAreaYDilation: 0,
-    mouseAreaXDilation: 0,
-    mouseAreaYDilation: 0,
-
-    // PhET-iO
-    tandem: Tandem.REQUIRED
-  }, options );
-
-  // validate options
-  assert && assert( _.includes( ARROWS_POSITION_VALUES, options.arrowsPosition ), 'invalid arrowsPosition: ' + options.arrowsPosition );
-  assert && assert( _.includes( VALUE_ALIGN_VALUES, options.valueAlign ), 'invalid valueAlign: ' + options.valueAlign );
-  assert && assert( !!phet.chipper.queryParameters.stringTest ||
-                    options.valuePattern.indexOf( SunConstants.VALUE_NAMED_PLACEHOLDER ) !== -1,
-    'missing value placeholder in options.valuePattern: ' + options.valuePattern );
-
-  const self = this;
-
-  const valueOptions = {
-    font: options.font,
-    fill: 'black'
-  };
-
-  // compute max width of the value that's going to be displayed
-  const minString = StringUtils.fillIn( options.valuePattern, {
-    value: Utils.toFixed( rangeProperty.value.min, options.decimalPlaces )
-  } );
-  const maxString = StringUtils.fillIn( options.valuePattern, {
-    value: Utils.toFixed( rangeProperty.value.max, options.decimalPlaces )
-  } );
-  const maxWidth = Math.max(
-    new Text( minString, valueOptions ).width,
-    new Text( maxString, valueOptions ).width
-  );
-
-  // number
-  const numberNode = new Text( numberProperty.get(), valueOptions );
-
-  // compute the size of the background
-  const backgroundWidth = Math.max( maxWidth + 2 * options.xMargin, options.backgroundMinWidth );
-  const backgroundHeight = numberNode.height + ( 2 * options.yMargin );
-
-  // background for displaying the value
-  const backgroundNode = new Rectangle( 0, 0, backgroundWidth, backgroundHeight,
-    options.cornerRadius, options.cornerRadius, {
-      fill: options.backgroundFill,
-      stroke: options.backgroundStroke,
-      lineWidth: options.backgroundLineWidth
+class NumberSpinner extends Node {
+
+  /**
+   * @param {Property.<number>} numberProperty value, must be an integer
+   * @param {Property.<Range>} rangeProperty - Dynamic range of values, min and max must be integers
+   * @param {Object} [options]
+   * @mixes AccessibleNumberSpinner
+   */
+  constructor( numberProperty, rangeProperty, options ) {
+
+    assert && assert( rangeProperty.value.contains( numberProperty.get() ),
+      'value ' + numberProperty.get() + ' is out of range ' + rangeProperty.value.toString() );
+
+    options = merge( {
+      enabledProperty: new Property( true ),
+
+      // {string} where to place the arrow buttons, see ARROWS_POSITION_VALUES
+      arrowsPosition: 'bothRight',
+
+      // {number|null} By default, arrows are scaled to fit dimensions of value background. This is an additional scale factor.
+      arrowsScale: null,
+      arrowButtonFill: 'white',
+      arrowButtonStroke: 'black',
+      arrowButtonLineWidth: 1,
+
+      // {function|null} function called when the increment button is pressed, defaults to adding options.deltaValue
+      incrementFunction: null,
+
+      // {function|null} function called when the decrement button is pressed, defaults to subtracting options.deltaValue
+      decrementFunction: null,
+
+      valuePattern: SunConstants.VALUE_NAMED_PLACEHOLDER, // {string} must contain SunConstants.VALUE_NAMED_PLACEHOLDER
+      decimalPlaces: 0,
+      deltaValue: 1, // may be ignored if incrementFunction and decrementFunction are provided
+      font: new PhetFont( 28 ),
+
+      // {string} alignment for value, see VALUE_ALIGN_VALUES
+      valueAlign: 'center',
+      xSpacing: 5,
+      ySpacing: 3,
+
+      // background node
+      xMargin: 5,
+      yMargin: 3,
+      cornerRadius: 5,
+      backgroundMinWidth: 0,
+      backgroundFill: 'white',
+      backgroundStroke: 'black',
+      backgroundLineWidth: 1,
+
+      // arrow button pointer areas
+      touchAreaXDilation: 0,
+      touchAreaYDilation: 0,
+      mouseAreaXDilation: 0,
+      mouseAreaYDilation: 0,
+
+      // PhET-iO
+      tandem: Tandem.REQUIRED
+    }, options );
+
+    // validate options
+    assert && assert( _.includes( ARROWS_POSITION_VALUES, options.arrowsPosition ), 'invalid arrowsPosition: ' + options.arrowsPosition );
+    assert && assert( _.includes( VALUE_ALIGN_VALUES, options.valueAlign ), 'invalid valueAlign: ' + options.valueAlign );
+    assert && assert( !!phet.chipper.queryParameters.stringTest ||
+                      options.valuePattern.indexOf( SunConstants.VALUE_NAMED_PLACEHOLDER ) !== -1,
+      'missing value placeholder in options.valuePattern: ' + options.valuePattern );
+
+    const valueOptions = {
+      font: options.font,
+      fill: 'black'
+    };
+
+    // compute max width of the value that's going to be displayed
+    const minString = StringUtils.fillIn( options.valuePattern, {
+      value: Utils.toFixed( rangeProperty.value.min, options.decimalPlaces )
     } );
-  numberNode.center = backgroundNode.center;
-  const valueParent = new Node( { children: [ backgroundNode, numberNode ] } );
-
-  // buttons
-  const arrowButtonOptions = {
-    baseColor: options.arrowButtonFill,
-    stroke: options.arrowButtonStroke,
-    lineWidth: options.arrowButtonLineWidth,
-    focusable: false,
-
-    // as requested in https://github.com/phetsims/sun/issues/575
-    enabledPropertyOptions: {
-      phetioReadOnly: true,
-      phetioFeatured: false
-    }
-  };
+    const maxString = StringUtils.fillIn( options.valuePattern, {
+      value: Utils.toFixed( rangeProperty.value.max, options.decimalPlaces )
+    } );
+    const maxWidth = Math.max(
+      new Text( minString, valueOptions ).width,
+      new Text( maxString, valueOptions ).width
+    );
+
+    // number
+    const numberNode = new Text( numberProperty.get(), valueOptions );
+
+    // compute the size of the background
+    const backgroundWidth = Math.max( maxWidth + 2 * options.xMargin, options.backgroundMinWidth );
+    const backgroundHeight = numberNode.height + ( 2 * options.yMargin );
+
+    // background for displaying the value
+    const backgroundNode = new Rectangle( 0, 0, backgroundWidth, backgroundHeight,
+      options.cornerRadius, options.cornerRadius, {
+        fill: options.backgroundFill,
+        stroke: options.backgroundStroke,
+        lineWidth: options.backgroundLineWidth
+      } );
+    numberNode.center = backgroundNode.center;
+    const valueParent = new Node( { children: [ backgroundNode, numberNode ] } );
+
+    // buttons
+    const arrowButtonOptions = {
+      baseColor: options.arrowButtonFill,
+      stroke: options.arrowButtonStroke,
+      lineWidth: options.arrowButtonLineWidth,
+      focusable: false,
+
+      // as requested in https://github.com/phetsims/sun/issues/575
+      enabledPropertyOptions: {
+        phetioReadOnly: true,
+        phetioFeatured: false
+      }
+    };
 
   // increment button
   const incrementFunction = options.incrementFunction || function() {
@@ -167,148 +165,148 @@ function NumberSpinner( numberProperty, rangeProperty, options ) {
     tandem: options.tandem.createTandem( 'decrementButton' )
   }, arrowButtonOptions ) );
 
-  // arrow button scaling
-  let arrowsScale;
-  if ( !arrowsScale ) {
+    // arrow button scaling
+    let arrowsScale;
+    if ( !arrowsScale ) {
+      if ( options.arrowsPosition === 'leftRight' ) {
+        arrowsScale = valueParent.height / incrementButton.height;
+      }
+      else if ( options.arrowsPosition === 'topBottom' ) {
+        arrowsScale = valueParent.width / incrementButton.width;
+      }
+      else if ( options.arrowsPosition === 'bothRight' ) {
+        arrowsScale = ( ( valueParent.height / 2 ) - ( options.ySpacing / 2 ) ) / incrementButton.height;
+      }
+      else { // 'bothBottom'
+        arrowsScale = ( ( valueParent.width / 2 ) - ( options.xSpacing / 2 ) ) / incrementButton.width;
+      }
+    }
+    if ( options.arrowsScale ) {
+      arrowsScale = arrowsScale * options.arrowsScale;
+    }
+    incrementButton.setScaleMagnitude( arrowsScale );
+    decrementButton.setScaleMagnitude( arrowsScale );
+
+    // layout
     if ( options.arrowsPosition === 'leftRight' ) {
-      arrowsScale = valueParent.height / incrementButton.height;
+      incrementButton.left = valueParent.right + options.xSpacing;
+      decrementButton.right = valueParent.left - options.xSpacing;
+      incrementButton.centerY = decrementButton.centerY = valueParent.centerY;
     }
     else if ( options.arrowsPosition === 'topBottom' ) {
-      arrowsScale = valueParent.width / incrementButton.width;
+      incrementButton.centerX = decrementButton.centerX = valueParent.centerX;
+      incrementButton.bottom = valueParent.top - options.ySpacing;
+      decrementButton.top = valueParent.bottom + options.ySpacing;
     }
     else if ( options.arrowsPosition === 'bothRight' ) {
-      arrowsScale = ( ( valueParent.height / 2 ) - ( options.ySpacing / 2 ) ) / incrementButton.height;
+      incrementButton.left = decrementButton.left = valueParent.right + options.xSpacing;
+      incrementButton.bottom = valueParent.centerY - ( options.ySpacing / 2 );
+      decrementButton.top = valueParent.centerY + ( options.ySpacing / 2 );
     }
     else { // 'bothBottom'
-      arrowsScale = ( ( valueParent.width / 2 ) - ( options.xSpacing / 2 ) ) / incrementButton.width;
-    }
-  }
-  if ( options.arrowsScale ) {
-    arrowsScale = arrowsScale * options.arrowsScale;
-  }
-  incrementButton.setScaleMagnitude( arrowsScale );
-  decrementButton.setScaleMagnitude( arrowsScale );
-
-  // layout
-  if ( options.arrowsPosition === 'leftRight' ) {
-    incrementButton.left = valueParent.right + options.xSpacing;
-    decrementButton.right = valueParent.left - options.xSpacing;
-    incrementButton.centerY = decrementButton.centerY = valueParent.centerY;
-  }
-  else if ( options.arrowsPosition === 'topBottom' ) {
-    incrementButton.centerX = decrementButton.centerX = valueParent.centerX;
-    incrementButton.bottom = valueParent.top - options.ySpacing;
-    decrementButton.top = valueParent.bottom + options.ySpacing;
-  }
-  else if ( options.arrowsPosition === 'bothRight' ) {
-    incrementButton.left = decrementButton.left = valueParent.right + options.xSpacing;
-    incrementButton.bottom = valueParent.centerY - ( options.ySpacing / 2 );
-    decrementButton.top = valueParent.centerY + ( options.ySpacing / 2 );
-  }
-  else { // 'bothBottom'
-    incrementButton.left = valueParent.centerX + ( options.xSpacing / 2 );
-    decrementButton.right = valueParent.centerX - ( options.xSpacing / 2 );
-    incrementButton.top = decrementButton.top = valueParent.bottom + options.ySpacing;
-  }
-
-  // touch areas
-  if ( options.touchAreaXDilation || options.touchAreaYDilation ) {
-
-    incrementButton.touchArea = incrementButton.localBounds.dilatedXY( options.touchAreaXDilation, options.touchAreaYDilation );
-    decrementButton.touchArea = decrementButton.localBounds.dilatedXY( options.touchAreaXDilation, options.touchAreaYDilation );
-
-    // shift touch areas for these options, to prevent overlap
-    if ( options.arrowsPosition === 'bothRight' ) {
-      incrementButton.touchArea = incrementButton.touchArea.shiftedY( -options.touchAreaYDilation );
-      decrementButton.touchArea = decrementButton.touchArea.shiftedY( options.touchAreaYDilation );
+      incrementButton.left = valueParent.centerX + ( options.xSpacing / 2 );
+      decrementButton.right = valueParent.centerX - ( options.xSpacing / 2 );
+      incrementButton.top = decrementButton.top = valueParent.bottom + options.ySpacing;
     }
-    else if ( options.arrowsPosition === 'bothBottom' ) {
-      incrementButton.touchArea = incrementButton.touchArea.shiftedX( options.touchAreaXDilation );
-      decrementButton.touchArea = decrementButton.touchArea.shiftedX( -options.touchAreaXDilation );
-    }
-  }
-
-  // mouse areas
-  if ( options.mouseAreaXDilation || options.mouseAreaYDilation ) {
 
-    incrementButton.mouseArea = incrementButton.localBounds.dilatedXY( options.mouseAreaXDilation, options.mouseAreaYDilation );
-    decrementButton.mouseArea = decrementButton.localBounds.dilatedXY( options.mouseAreaXDilation, options.mouseAreaYDilation );
-
-    // shift touch areas for these options, to prevent overlap
-    if ( options.arrowsPosition === 'bothRight' ) {
-      incrementButton.mouseArea = incrementButton.mouseArea.shiftedY( -options.mouseAreaYDilation );
-      decrementButton.mouseArea = decrementButton.mouseArea.shiftedY( options.mouseAreaYDilation );
-    }
-    else if ( options.arrowsPosition === 'bothBottom' ) {
-      incrementButton.mouseArea = incrementButton.mouseArea.shiftedX( options.mouseAreaXDilation );
-      decrementButton.mouseArea = decrementButton.mouseArea.shiftedX( -options.mouseAreaXDilation );
+    // touch areas
+    if ( options.touchAreaXDilation || options.touchAreaYDilation ) {
+
+      incrementButton.touchArea = incrementButton.localBounds.dilatedXY( options.touchAreaXDilation, options.touchAreaYDilation );
+      decrementButton.touchArea = decrementButton.localBounds.dilatedXY( options.touchAreaXDilation, options.touchAreaYDilation );
+
+      // shift touch areas for these options, to prevent overlap
+      if ( options.arrowsPosition === 'bothRight' ) {
+        incrementButton.touchArea = incrementButton.touchArea.shiftedY( -options.touchAreaYDilation );
+        decrementButton.touchArea = decrementButton.touchArea.shiftedY( options.touchAreaYDilation );
+      }
+      else if ( options.arrowsPosition === 'bothBottom' ) {
+        incrementButton.touchArea = incrementButton.touchArea.shiftedX( options.touchAreaXDilation );
+        decrementButton.touchArea = decrementButton.touchArea.shiftedX( -options.touchAreaXDilation );
+      }
     }
-  }
 
-  assert && assert( !options.children, 'decoration not supported' );
-  options.children = [ valueParent, incrementButton, decrementButton ];
-
-  Node.call( this, options );
-
-  const updateEnabled = function() {
-    // enable/disable arrow buttons
-    incrementButton.enabled = ( ( numberProperty.value + options.deltaValue ) <= rangeProperty.value.max );
-    decrementButton.enabled = ( ( numberProperty.value - options.deltaValue ) >= rangeProperty.value.min );
-  };
-
-  // synchronize with number value
-  const numberPropertyObserver = function( value ) {
-    assert && assert( rangeProperty.value.contains( value ), 'value out of range: ' + value );
-
-    // update the number
-    numberNode.text = StringUtils.fillIn( options.valuePattern, {
-      value: Utils.toFixed( value, options.decimalPlaces )
-    } );
-
-    // update the alignment
-    switch( options.valueAlign ) {
-      case 'center':
-        numberNode.center = backgroundNode.center;
-        break;
-      case 'left':
-        numberNode.left = backgroundNode.left + options.xMargin;
-        break;
-      case 'right':
-        numberNode.right = backgroundNode.right - options.xMargin;
-        break;
-      default:
-        throw new Error( 'invalid valueAlign: ' + options.valueAlign );
+    // mouse areas
+    if ( options.mouseAreaXDilation || options.mouseAreaYDilation ) {
+
+      incrementButton.mouseArea = incrementButton.localBounds.dilatedXY( options.mouseAreaXDilation, options.mouseAreaYDilation );
+      decrementButton.mouseArea = decrementButton.localBounds.dilatedXY( options.mouseAreaXDilation, options.mouseAreaYDilation );
+
+      // shift touch areas for these options, to prevent overlap
+      if ( options.arrowsPosition === 'bothRight' ) {
+        incrementButton.mouseArea = incrementButton.mouseArea.shiftedY( -options.mouseAreaYDilation );
+        decrementButton.mouseArea = decrementButton.mouseArea.shiftedY( options.mouseAreaYDilation );
+      }
+      else if ( options.arrowsPosition === 'bothBottom' ) {
+        incrementButton.mouseArea = incrementButton.mouseArea.shiftedX( options.mouseAreaXDilation );
+        decrementButton.mouseArea = decrementButton.mouseArea.shiftedX( -options.mouseAreaXDilation );
+      }
     }
 
-    updateEnabled();
-  };
-  numberProperty.link( numberPropertyObserver ); // must be unlinked in dispose
-
-  // Dynamic range changes, see https://github.com/phetsims/scenery-phet/issues/305
-  const rangeObserver = function( range ) {
-    // If our value is outside our new range, adjust it to be within the range.
-    numberProperty.value = range.constrainValue( numberProperty.value );
-
-    // Range changes may change whether the buttons are enabled
-    updateEnabled();
-  };
-  rangeProperty.link( rangeObserver );
-
-  // enable or disable this component
-  this.enabledProperty = options.enabledProperty; // @public
-  const enabledPropertyObserver = function( enabled ) {
-    self.pickable = enabled;
-    self.opacity = enabled ? 1 : 0.5;
-    //TODO if !enabled, cancel any interaction that is in progress, see scenery#218
-  };
-  this.enabledProperty.link( enabledPropertyObserver );
-
-  // a11y - initialize accessibility features
-  assert && assert( !options.keyboardStep, 'keyboardStep supported by arrow buttons, do not pass value to NumberSpinner' );
-  assert && assert( !options.shiftKeyboardStep, 'shiftKeyboardStep handled by arrow buttons' );
-  options.keyboardStep = 0;
-  options.shiftKeyboardStep = 0;
-  this.initializeAccessibleNumberSpinner( numberProperty, rangeProperty, this.enabledProperty, options );
+    assert && assert( !options.children, 'decoration not supported' );
+    options.children = [ valueParent, incrementButton, decrementButton ];
+
+    super( options );
+
+    const updateEnabled = () => {
+      // enable/disable arrow buttons
+      incrementButton.enabled = ( ( numberProperty.value + options.deltaValue ) <= rangeProperty.value.max );
+      decrementButton.enabled = ( ( numberProperty.value - options.deltaValue ) >= rangeProperty.value.min );
+    };
+
+    // synchronize with number value
+    const numberPropertyObserver = value => {
+      assert && assert( rangeProperty.value.contains( value ), 'value out of range: ' + value );
+
+      // update the number
+      numberNode.text = StringUtils.fillIn( options.valuePattern, {
+        value: Utils.toFixed( value, options.decimalPlaces )
+      } );
+
+      // update the alignment
+      switch( options.valueAlign ) {
+        case 'center':
+          numberNode.center = backgroundNode.center;
+          break;
+        case 'left':
+          numberNode.left = backgroundNode.left + options.xMargin;
+          break;
+        case 'right':
+          numberNode.right = backgroundNode.right - options.xMargin;
+          break;
+        default:
+          throw new Error( 'invalid valueAlign: ' + options.valueAlign );
+      }
+
+      updateEnabled();
+    };
+    numberProperty.link( numberPropertyObserver ); // must be unlinked in dispose
+
+    // Dynamic range changes, see https://github.com/phetsims/scenery-phet/issues/305
+    const rangeObserver = range => {
+      // If our value is outside our new range, adjust it to be within the range.
+      numberProperty.value = range.constrainValue( numberProperty.value );
+
+      // Range changes may change whether the buttons are enabled
+      updateEnabled();
+    };
+    rangeProperty.link( rangeObserver );
+
+    // enable or disable this component
+    this.enabledProperty = options.enabledProperty; // @public
+    const enabledPropertyObserver = enabled => {
+      this.pickable = enabled;
+      this.opacity = enabled ? 1 : 0.5;
+      //TODO if !enabled, cancel any interaction that is in progress, see scenery#218
+    };
+    this.enabledProperty.link( enabledPropertyObserver );
+
+    // a11y - initialize accessibility features
+    assert && assert( !options.keyboardStep, 'keyboardStep supported by arrow buttons, do not pass value to NumberSpinner' );
+    assert && assert( !options.shiftKeyboardStep, 'shiftKeyboardStep handled by arrow buttons' );
+    options.keyboardStep = 0;
+    options.shiftKeyboardStep = 0;
+    this.initializeAccessibleNumberSpinner( numberProperty, rangeProperty, this.enabledProperty, options );
 
   // a11y - click arrow buttons on keyboard increment/decrement; must be disposed
   const increasedListener = function( isDown ) { isDown && incrementButton.a11yClick(); };
@@ -316,43 +314,43 @@ function NumberSpinner( numberProperty, rangeProperty, options ) {
   this.incrementDownEmitter.addListener( increasedListener );
   this.decrementDownEmitter.addListener( decreasedListener );
 
-  // Create a link to associated Property, so it's easier to find in Studio.
-  this.addLinkedElement( numberProperty, {
-    tandem: options.tandem.createTandem( 'property' )
-  } );
-
-  // @private
-  this.disposeNumberSpinner = function() {
+    // Create a link to associated Property, so it's easier to find in Studio.
+    this.addLinkedElement( numberProperty, {
+      tandem: options.tandem.createTandem( 'property' )
+    } );
 
-    // dispose a11y features
-    self.incrementDownEmitter.removeListener( increasedListener );
-    self.decrementDownEmitter.removeListener( decreasedListener );
-    self.disposeAccessibleNumberSpinner();
+    // @private
+    this.disposeNumberSpinner = () => {
 
-    numberProperty.unlink( numberPropertyObserver );
-    rangeProperty.unlink( rangeObserver );
-    self.enabledProperty.unlink( enabledPropertyObserver );
-  };
-}
+      // dispose a11y features
+      this.incrementDownEmitter.removeListener( increasedListener );
+      this.decrementDownEmitter.removeListener( decreasedListener );
+      this.disposeAccessibleNumberSpinner();
 
-sun.register( 'NumberSpinner', NumberSpinner );
-
-inherit( Node, NumberSpinner, {
+      numberProperty.unlink( numberPropertyObserver );
+      rangeProperty.unlink( rangeObserver );
+      this.enabledProperty.unlink( enabledPropertyObserver );
+    };
+  }
 
   // @public Ensures that this node is eligible for GC.
-  dispose: function() {
+  dispose() {
     this.disposeNumberSpinner();
     Node.prototype.dispose.call( this );
-  },
+  }
 
   // @public
-  setEnabled: function( enabled ) { this.enabledProperty.set( enabled ); },
-  set enabled( value ) { this.setEnabled( value ); },
+  setEnabled( enabled ) { this.enabledProperty.set( enabled ); }
+
+  set enabled( value ) { this.setEnabled( value ); }
 
   // @public
-  getEnabled: function() { return this.enabledProperty.get(); },
+  getEnabled() { return this.enabledProperty.get(); }
+
   get enabled() { return this.getEnabled(); }
-} );
+}
+
+sun.register( 'NumberSpinner', NumberSpinner );
 
 AccessibleNumberSpinner.mixInto( NumberSpinner );