https://www.codewars.com/kata/undo-slash-redo/train/javascript

redoUndo.js

function undoRedo(object) {
  //var storage = object;
  var actions = [];  // keep track of action performed
  // action schema -> { name, params, has_undone }
  // for non-undo acton, example of params { key, value }
  // for undo action, example of params { action, key, value }

  var findLastAction = function(status) {
    var lastAction = null; 
    for (var i = actions.length - 1; i >= 0; i--) {
     var action = actions[i];
     if ((action.name === 'del' || action.name === 'set') && action.has_undone === status) {
       lastAction = action;
       return lastAction;
     }
    }
    return null;
  }
  
  var redoUndoSet = function(lastAction) {
    if (lastAction.params.old_value != null && typeof lastAction.params.old_value !== 'undefined') { 
      object[lastAction.params.key] = lastAction.params.old_value;
    } else {
      delete object[lastAction.params.key];
    }
  }
    
  return {
		set: function(key, value) {
      var oldvalue = undefined;
      if (object[key]) {
        oldvalue = object[key];
      } 
      object[key] = value;
      actions.push( { name: 'set', has_undone: false, params: { key: key, old_value: oldvalue, new_value: value } } );
    },
		get: function(key) {
      return object[key];
    },
		del: function(key) {
      if (object[key]) {
        var value = object[key];
        actions.push( { name: 'del', has_undone: false, params: { key: key, old_value: value, new_value: undefined } } );
        delete object[key];
      }
    },
		undo: function() {
        // look for last set/del action, perform it and push undo action in stack
        if (actions.length > 0) {
         var lastAction = findLastAction(false); 
         if (lastAction) {
            lastAction.has_undone = true;
            if (lastAction.name === 'set') {
              redoUndoSet(lastAction);
              actions.push({ name: 'undo',
                params: { action: 'set', 
                          key: lastAction.params.key, 
                          old_value: lastAction.params.new_value,
                          new_value: lastAction.params.old_value } }); 
            } else if (lastAction.name === 'del') {
              // perform set 
              object[lastAction.params.key] = lastAction.params.old_value;
              actions.push({ name: 'undo',
                params: { action: 'set', 
                      key: lastAction.params.key, 
                      old_value: undefined,
                      new_value: lastAction.params.old_value  } }); 
            } 
          } else {
              throw new Error();
          }
        } else {
          throw new Error('no action to undo');          
        }
    },
		redo: function() {
        // check if last action is undo
        if (actions.length > 0) {  
          var lastAction = actions[actions.length - 1];
          if (lastAction.name === 'undo') {
            var lastDelSetAction = findLastAction(true);
            if (lastDelSetAction) {
              lastDelSetAction.has_undone = false;
            }
            if (lastAction.params.action === 'set') {
              redoUndoSet(lastAction);
              // pop the last undo action
              actions.splice(actions.length - 1, 1);
            } else if (lastAction.params.action === 'delete') {
              // redo set
              object[lastAction.params.key] = lastAction.params.old_value;
              // pop the last undo action
              actions.splice(actions.length - 1, 1);
            }
          } else {
            throw new Error ('Redo is not immediately after Undo');
          }
        } else {
          throw new Error('no action to redo');
        }
    }
	};
}