cleanup: Port non-GObject classes to JS6 classes

ES6 finally adds standard class syntax to the language, so we can
replace our custom Lang.Class framework with the new syntax. Any
classes that inherit from GObject will need special treatment,
so limit the port to regular javascript classes for now.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/361

js/ui/slider.js

@@ -3,7 +3,6 @@
 const Atk = imports.gi.Atk;
 const Cairo = imports.cairo;
 const Clutter = imports.gi.Clutter;
-const Lang = imports.lang;
 const St = imports.gi.St;
 const Signals = imports.signals;
 
@@ -11,18 +10,15 @@ const BarLevel = imports.ui.barLevel;
 
 var SLIDER_SCROLL_STEP = 0.02; /* Slider scrolling step in % */
 
-var Slider = new Lang.Class({
-    Name: "Slider",
-    Extends: BarLevel.BarLevel,
-
-    _init(value) {
+var Slider = class extends BarLevel.BarLevel {
+    constructor(value) {
         let params = {
             styleClass: 'slider',
             canFocus: true,
             reactive: true,
             accessibleRole: Atk.Role.SLIDER,
         }
-        this.parent(value, params)
+        super(value, params)
 
         this.actor.connect('button-press-event', this._startDragging.bind(this));
         this.actor.connect('touch-event', this._touchDragging.bind(this));
@@ -33,10 +29,10 @@ var Slider = new Lang.Class({
         this._dragging = false;
 
         this._customAccessible.connect('get-minimum-increment', this._getMinimumIncrement.bind(this));
-    },
+    }
 
     _barLevelRepaint(area) {
-        this.parent(area);
+        super._barLevelRepaint(area);
 
         // Add handle
         let cr = area.get_context();
@@ -64,11 +60,11 @@ var Slider = new Lang.Class({
             cr.stroke();
         }
         cr.$dispose();
-    },
+    }
 
     _startDragging(actor, event) {
         return this.startDragging(event);
-    },
+    }
 
     startDragging(event) {
         if (this._dragging)
@@ -100,7 +96,7 @@ var Slider = new Lang.Class({
         [absX, absY] = event.get_coords();
         this._moveHandle(absX, absY);
         return Clutter.EVENT_STOP;
-    },
+    }
 
     _endDragging() {
         if (this._dragging) {
@@ -121,7 +117,7 @@ var Slider = new Lang.Class({
             this.emit('drag-end');
         }
         return Clutter.EVENT_STOP;
-    },
+    }
 
     _touchDragging(actor, event) {
         let device = event.get_device();
@@ -139,7 +135,7 @@ var Slider = new Lang.Class({
         }
 
         return Clutter.EVENT_PROPAGATE;
-    },
+    }
 
     scroll(event) {
         let direction = event.get_scroll_direction();
@@ -164,18 +160,18 @@ var Slider = new Lang.Class({
         this.actor.queue_repaint();
         this.emit('value-changed', this._value);
         return Clutter.EVENT_STOP;
-    },
+    }
 
     _onScrollEvent(actor, event) {
         return this.scroll(event);
-    },
+    }
 
     _motionEvent(actor, event) {
         let absX, absY;
         [absX, absY] = event.get_coords();
         this._moveHandle(absX, absY);
         return Clutter.EVENT_STOP;
-    },
+    }
 
     onKeyPressEvent(actor, event) {
         let key = event.get_key_symbol();
@@ -189,7 +185,7 @@ var Slider = new Lang.Class({
             return Clutter.EVENT_STOP;
         }
         return Clutter.EVENT_PROPAGATE;
-    },
+    }
 
     _moveHandle(absX, absY) {
         let relX, relY, sliderX, sliderY;
@@ -210,11 +206,10 @@ var Slider = new Lang.Class({
         this._value = newvalue * this._maxValue;
         this.actor.queue_repaint();
         this.emit('value-changed', this._value);
-    },
+    }
 
     _getMinimumIncrement(actor) {
         return 0.1;
-    },
-});
-
+    }
+};
 Signals.addSignalMethods(Slider.prototype);