Can't send a message via custom store/dispatch in botframework-webchat for IE11/es5

My customer requires IE11 support for our chatbot. I had to modify the webchat code not to use es6 features like arrow functions, as they are not supported in IE11/es5. For the most part I was successful, but the one thing I wasn't able to get working was sending a message event I am sending. The new code works in Chrome, but I am getting an Expected identifier error message in IE11. Here is the relevant code:

const store = window.WebChat.createStore({}, function({dispatch}) { return function(next) { return function(action) {
    if (action.type === 'WEB_CHAT/SEND_MESSAGE') {
        // Message sent by the user
        PageTitleNotification.Off();
        clearTimeout(interval);
    } else if (action.type === 'DIRECT_LINE/INCOMING_ACTIVITY' && action.payload.activity.name !== "inactive") {
        // Message sent by the bot
        clearInterval(interval);
        interval = setTimeout(function() {
            // Change title to flash the page
            PageTitleNotification.On('Are you still there?');

            // Notify bot the user has been inactive
            dispatch({
                type: 'WEB_CHAT/SEND_EVENT',
                payload: {
                    name: 'inactive',
                    value: ''
                }
            });

        }, 3000)
    }
    return next(action);
}}});

Previously the first line looked like

const store = window.WebChat.createStore({}, ({ dispatch }) => next => action => {

The issue is coming at function({dispatch}). IE console is saying an identifier is expected and the entire webchat fails to load. It works fine in Chrome. If I change function({dispatch}) to just function(dispatch), the bot renders but the dispatch statement sending the inactive message to the bot (below) no longer functions in IE OR Chrome.

// Notify bot the user has been inactive
dispatch({
    type: 'WEB_CHAT/SEND_EVENT',
    payload: {
        name: 'inactive',
        value: ''
    }
});

Why is IE not recognizing {dispatch} as an identifier, and what can I do to get this working?

IE11 doesn't support that syntax. ES6 allows to set object properties by variable name, so the ES5 equivalent is:

window.WebChat.createStore({}, { dispatch: dispatch }) {
  // ...
}

Edit:

After some debugging, the final solution was to pass in just the dispatch object to the createStore function directly, and accessing its dispatch method:

dispatch.dispatch({
    type: 'WEB_CHAT/SEND_EVENT',
    payload: {
        name: 'inactive',
        value: ''
    }
});

You could rename the argument to reduce redundancy but it's not needed.