feat: Add middleClick helper

Author: rstoenescu

src/directives/touch-hold.js

@@ -17,7 +17,7 @@ export default {
 
     let ctx = {
       mouseStart (evt) {
-        if (mouse && leftClick(evt)) {
+        if (leftClick(evt)) {
           document.addEventListener('mousemove', ctx.mouseAbort)
           document.addEventListener('mouseup', ctx.mouseAbort)
           ctx.start(evt)

src/directives/touch-pan.js

@@ -97,7 +97,7 @@ export default {
       direction: getDirection(binding.modifiers),
 
       mouseStart (evt) {
-        if (mouse && leftClick(evt)) {
+        if (leftClick(evt)) {
           document.addEventListener('mousemove', ctx.mouseMove)
           document.addEventListener('mouseup', ctx.mouseEnd)
           ctx.start(evt)

src/directives/touch-swipe.js

@@ -53,7 +53,7 @@ export default {
       direction: getDirection(binding.modifiers),
 
       mouseStart (evt) {
-        if (mouse && leftClick(evt)) {
+        if (leftClick(evt)) {
           document.addEventListener('mousemove', ctx.mouseMove)
           document.addEventListener('mouseup', ctx.mouseEnd)
           ctx.start(evt)

src/utils/event.js

@@ -2,6 +2,10 @@ export function leftClick (e = window.event) {
   return e.button === 0
 }
 
+export function middleClick (e = window.event) {
+  return e.button === 1
+}
+
 export function rightClick (e = window.event) {
   return e.button === 2
 }