Firebase cloud function for Slack button actions in medium article https://medium.com/evenbit/151c1c98641d

http_trigger.ts

export const message_action = functions.https.onRequest(async (request, response) => {
    if (request.method !== "POST") {
        console.error(`Got unsupported ${request.method} request. Expected POST.`);
        return response.send(405, "Only POST requests are accepted");
    }

    if (!request.body && request.body.payload) {
        return response.send(405, "Expected a message action payload.");
    }

    const action = JSON.parse(request.body.payload);

    if (action.callback_id !== SLACK_ACTION_REQUEST_PING) {
        return response.send(405, "Only ping pong actions are implemented!");
    }

    // Handle the actions later, Slack expect this request to return within 3000ms
    await admin.database().ref("actions").push(action);

    // Update the buttons to try and limit the amount of player inputs
    if (action.actions[0].name.startsWith("1")) {
        action.original_message.attachments[0].actions[0].style = "primary";
        action.original_message.attachments[0].actions[0].name = "2.pong";
    } else if (action.actions[0].name.startsWith("2")) {
        action.original_message.attachments[0].actions[0].style = "danger";
        action.original_message.attachments[0].actions[0].name = "3.pong";
    } else {
        action.original_message.text = `The current game of PING (id ${action.actions[0].value}) is over!`;
        action.original_message.attachments[0].actions = [];
    }

    return response.contentType("json").status(200).send(action.original_message);
});