Adds check to make sure we do not add a new tile if you ca not slide.

main.js

@@ -13,33 +13,49 @@ const btnGo_onClick = () => {
 
 const btnUp_onClick = () => {
     const grid = globals.grid;
+    if (canSlideUp(grid)) {
         slideUp(grid);
         addRandomTile();
         redraw(grid)
+    } else {
+        alert('Unable to slide Up.');
+    }
     // alert('Up');
 }
 
 const btnDown_onClick = () => {
     const grid = globals.grid;
+    if (canSlideDown(grid)) {
         slideDown(grid);
         addRandomTile();
         redraw(grid)
+    } else {
+        alert('Unable to slide Down.');
+    }
     // alert('Down');
 }
 
 const btnLeft_onClick = () => {
     const grid = globals.grid;
+    if (canSlideLeft(grid)) {
         slideLeft(grid);
         addRandomTile();
         redraw(grid)
+    } else {
+        alert('Unable to slide Left.');
+    }
     // alert('Left');
 }
 
 const btnRight_onClick = () => {
     const grid = globals.grid;
+    if (canSlideRight(grid)) {
         slideRight(grid);
         addRandomTile();
         redraw(grid)
+    } else {
+        alert('Unable to slide Right.');
+    }
     // alert('Right');
 }
 
@@ -181,3 +197,73 @@ const slideRight = (grid) => {
         }
     }
 }
+
+const canSlideUp = (grid) => {
+    canIDoIt = false;
+    for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
+        lastIndex = -1;
+        for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
+            const tile = grid.getTile(rowIndex, columnIndex);
+            if (tile.visible) {
+                lastIndex++;
+                if (lastIndex != rowIndex) {
+                    canIDoIt = true;
+                }
+            }
+        }
+    }
+    return canIDoIt;
+}
+
+const canSlideLeft = (grid) => {
+    let canIDoIt = false;
+    for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
+        lastIndex = -1;
+        for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
+            const tile = grid.getTile(rowIndex, columnIndex);
+            if (tile.visible) {
+                lastIndex++;
+                if (lastIndex != columnIndex) {
+                    canIDoIt = true;
+                }
+            }
+        }
+    }
+    return canIDoIt;
+}
+
+const canSlideDown = (grid) => {
+    let canIDoIt = false;
+    for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
+        lastIndex = grid.numRows;
+        for (let rowIndex = grid.numRows - 1; rowIndex >= 0; rowIndex -= 1) {
+            const tile = grid.getTile(rowIndex, columnIndex);
+            if (tile.visible) {
+                lastIndex--;
+                if (lastIndex != rowIndex) {
+                    canIDoIt = true;
+                }
+            }
+        }
+    }
+    return canIDoIt;
+
+}
+
+const canSlideRight = (grid) => {
+    let canIDoIt = false;
+    for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
+        lastIndex = grid.numColumns;
+        for (let columnIndex = grid.numColumns - 1; columnIndex >= 0; columnIndex -= 1) {
+            const tile = grid.getTile(rowIndex, columnIndex);
+            if (tile.visible) {
+                lastIndex--;
+                if (lastIndex != columnIndex) {
+                    canIDoIt = true;
+                }
+            }
+        }
+    }
+    return canIDoIt;
+}
+