Add support for negative positions

README.md

@@ -138,11 +138,25 @@ Get current tab icon URL / icon.
 
 #### `tab.setPosition(newPosition)`
 
-Move tab to the specified position.
+Move tab to the specified position. A negative value is an offset from the right.
 
-#### `tab.getPosition()`
+To move a tab to the leftmost position:
 
-Get the tab position.
+```javascript
+tab.setPosition(1);
+```
+
+> Note: a position of 0 also moves the tab to the leftmost position
+
+To move a tab to the rightmost position:
+
+```javascript
+tab.setPosition(-1);
+```
+
+#### `tab.getPosition(fromRight)`
+
+Get the tab position. If `fromRight` is true, then the index returned is negative and is the offset from the right.
 
 #### `tab.activate()`
 

index.js

@@ -209,6 +209,51 @@ class Tab extends EventEmitter {
         return this.icon;
     }
 
+    setPosition (newPosition) {
+        let tabContainer = this.tabGroup.tabContainer;
+        let tabs = tabContainer.children;
+        let oldPosition = this.getPosition();
+
+        if (newPosition < 0) {
+            newPosition += tabContainer.childElementCount;
+
+            if (newPosition < 0) {
+                newPosition = 0;
+            }
+        } else {
+            if (newPosition > tabContainer.childElementCount) {
+                newPosition = tabContainer.childElementCount;
+            }
+
+            // Make 1 be leftmost position
+            newPosition--;
+        }
+
+        if (newPosition > oldPosition) {
+            newPosition++;
+        }
+
+        tabContainer.insertBefore(tabs[oldPosition], tabs[newPosition]);
+
+        return this;
+    }
+
+    getPosition (fromRight) {
+        let position = 0;
+        let tab = this.tab;
+        while ((tab = tab.previousSibling) != null) position++;
+
+        if (fromRight === true) {
+            position -= this.tabGroup.tabContainer.childElementCount;
+        }
+
+        if (position === 0) {
+            position = 1;
+        }
+
+        return position;
+    }
+
     activate () {
         if (this.isClosed) return;
         let activeTab = this.tabGroup.getActiveTab();
@@ -271,27 +316,6 @@ class Tab extends EventEmitter {
             TabGroupPrivate.activateRecentTab.bind(tabGroup)();
         }
     }
-
-    getPosition () {
-        let i = 0;
-        let tab = this.tab;
-        while ((tab = tab.previousSibling) != null) i++;
-        return i;
-    }
-
-    setPosition (newPosition) {
-        let tabContainer = this.tabGroup.tabContainer;
-        let tabs = tabContainer.children;
-        let oldPosition = this.getPosition();
-
-        if (newPosition > oldPosition) {
-            newPosition++;
-        }
-
-        tabContainer.insertBefore(tabs[oldPosition], tabs[newPosition]);
-
-        return this;
-    }
 }
 
 const TabPrivate = {