Use passive event listeners for touch events

Avoid this warning in Chrome console: https://www.chromestatus.com/feature/5745543795965952

ui/static/js.go

@@ -9,7 +9,9 @@ static scrollPageTo(element){let windowScrollPosition=window.pageYOffset;let win
 static getVisibleElements(selector){let elements=document.querySelectorAll(selector);let result=[];for(let i=0;i<elements.length;i++){if(this.isVisible(elements[i])){result.push(elements[i]);}}
 return result;}
 static findParent(element,selector){for(;element&&element!==document;element=element.parentNode){if(element.classList.contains(selector)){return element;}}
-return null;}}
+return null;}
+static hasPassiveEventListenerOption(){var passiveSupported=false;try{var options=Object.defineProperty({},"passive",{get:function(){passiveSupported=true;}});window.addEventListener("test",options,options);window.removeEventListener("test",options,options);}catch(err){passiveSupported=false;}
+return passiveSupported;}}
 class TouchHandler{constructor(){this.reset();}
 reset(){this.touch={start:{x:-1,y:-1},move:{x:-1,y:-1},element:null};}
 calculateDistance(){if(this.touch.start.x>=-1&&this.touch.move.x>=-1){let horizontalDistance=Math.abs(this.touch.move.x-this.touch.start.x);let verticalDistance=Math.abs(this.touch.move.y-this.touch.start.y);if(horizontalDistance>30&&verticalDistance<70){return this.touch.move.x-this.touch.start.x;}}
@@ -24,7 +26,7 @@ onTouchEnd(event){if(event.touches===undefined){return;}
 if(this.touch.element!==null){let distance=Math.abs(this.calculateDistance());if(distance>75){EntryHandler.toggleEntryStatus(this.touch.element);}
 this.touch.element.style.opacity=1;this.touch.element.style.transform="none";}
 this.reset();}
-listen(){let elements=document.querySelectorAll(".touch-item");elements.forEach((element)=>{element.addEventListener("touchstart",(e)=>this.onTouchStart(e),false);element.addEventListener("touchmove",(e)=>this.onTouchMove(e),false);element.addEventListener("touchend",(e)=>this.onTouchEnd(e),false);element.addEventListener("touchcancel",()=>this.reset(),false);});}}
+listen(){let elements=document.querySelectorAll(".touch-item");let hasPassiveOption=DomHelper.hasPassiveEventListenerOption();elements.forEach((element)=>{element.addEventListener("touchstart",(e)=>this.onTouchStart(e),hasPassiveOption?{passive:true}:false);element.addEventListener("touchmove",(e)=>this.onTouchMove(e),hasPassiveOption?{passive:true}:false);element.addEventListener("touchend",(e)=>this.onTouchEnd(e),hasPassiveOption?{passive:true}:false);element.addEventListener("touchcancel",()=>this.reset(),hasPassiveOption?{passive:true}:false);});}}
 class KeyboardHandler{constructor(){this.queue=[];this.shortcuts={};}
 on(combination,callback){this.shortcuts[combination]=callback;}
 listen(){document.onkeydown=(event)=>{if(this.isEventIgnored(event)){return;}
@@ -93,5 +95,5 @@ document.addEventListener("DOMContentLoaded",function(){FormHandler.handleSubmit
 }
 
 var JavascriptChecksums = map[string]string{
-	"app": "c090bbc7f503aa032b4cfe68b58bc4754133aaed4f77ff768ac63f41528f55c3",
+	"app": "ef0457f301b924c25a20fa00e65bfda5437f41bc9ad0a0762b62b9c64b6d0ac5",
 }

ui/static/js/dom_helper.js

@@ -43,4 +43,23 @@ class DomHelper {
 
         return null;
     }
+
+    static hasPassiveEventListenerOption() {
+        var passiveSupported = false;
+
+        try {
+            var options = Object.defineProperty({}, "passive", {
+                get: function() {
+                    passiveSupported = true;
+                }
+            });
+
+            window.addEventListener("test", options, options);
+            window.removeEventListener("test", options, options);
+        } catch(err) {
+            passiveSupported = false;
+        }
+
+        return passiveSupported;
+    }
 }

ui/static/js/touch_handler.js

@@ -83,12 +83,13 @@ class TouchHandler {
 
     listen() {
         let elements = document.querySelectorAll(".touch-item");
+        let hasPassiveOption = DomHelper.hasPassiveEventListenerOption();
 
         elements.forEach((element) => {
-            element.addEventListener("touchstart", (e) => this.onTouchStart(e), false);
-            element.addEventListener("touchmove", (e) => this.onTouchMove(e), false);
-            element.addEventListener("touchend", (e) => this.onTouchEnd(e), false);
-            element.addEventListener("touchcancel", () => this.reset(), false);
+            element.addEventListener("touchstart", (e) => this.onTouchStart(e), hasPassiveOption ? { passive: true } : false);
+            element.addEventListener("touchmove", (e) => this.onTouchMove(e), hasPassiveOption ? { passive: true } : false);
+            element.addEventListener("touchend", (e) => this.onTouchEnd(e), hasPassiveOption ? { passive: true } : false);
+            element.addEventListener("touchcancel", () => this.reset(), hasPassiveOption ? { passive: true } : false);
         });
     }
 }