Prevent undo / redo if no past / future respectively

editor/utils/test/undoable-reducer.js

@@ -49,13 +49,43 @@ describe( 'undoableReducer', () => {
 			} );
 		} );
 
+		it( 'should not perform undo on empty past', () => {
+			const reducer = undoable( counter );
+
+			let state;
+			state = reducer( undefined, {} );
+			state = reducer( state, { type: 'INCREMENT' } );
+			state = reducer( state, { type: 'UNDO' } );
+
+			expect( state ).toEqual( {
+				past: [],
+				present: 0,
+				future: [ 1 ],
+			} );
+		} );
+
 		it( 'should perform redo', () => {
 			const reducer = undoable( counter );
 
 			let state;
 			state = reducer( undefined, {} );
 			state = reducer( state, { type: 'INCREMENT' } );
 			state = reducer( state, { type: 'UNDO' } );
+			state = reducer( state, { type: 'UNDO' } );
+
+			expect( state ).toEqual( {
+				past: [],
+				present: 0,
+				future: [ 1 ],
+			} );
+		} );
+
+		it( 'should not perform redo on empty future', () => {
+			const reducer = undoable( counter );
+
+			let state;
+			state = reducer( undefined, {} );
+			state = reducer( state, { type: 'INCREMENT' } );
 			state = reducer( state, { type: 'REDO' } );
 
 			expect( state ).toEqual( {

editor/utils/undoable-reducer.js

@@ -25,13 +25,23 @@ export function undoable( reducer, options = {} ) {
 
 		switch ( action.type ) {
 			case 'UNDO':
+				// Can't undo if no past
+				if ( ! past.length ) {
+					break;
+				}
+
 				return {
 					past: past.slice( 0, past.length - 1 ),
 					present: past[ past.length - 1 ],
 					future: [ present, ...future ],
 				};
 
 			case 'REDO':
+				// Can't redo if no future
+				if ( ! future.length ) {
+					break;
+				}
+
 				return {
 					past: [ ...past, present ],
 					present: future[ 0 ],