How to replace the buttons (attachment) only w/ Slack interactive buttons response - slack-api

Question

I've managed to create a simple interactive button Slack app using a Google Apps Script (GAS).
I know how to replace the original message w/ the response, but I would like to replace only the buttons, as demonstrated (but not clearly explained) multiple places in the Slack Interactive Button documentation:
https://api.slack.com/docs/message-buttons#crafting_your_message
I'd like to do what's demonstrated here:
https://a.slack-edge.com/dcb1/img/api/message_guidelines/Example_6.gif
Is this an update of the original message, a replacement of the original message with identical text but different attachment, ...?
My current interactive buttons message code looks like this:
function sendMsgWithButton() {
// slack channel url (where to send the message)
var slackUrl = "https://hooks.slack.com/services/...";
// message text
var messageData = {
"text": "Here's your interactive buttons message.",
"attachments": [
{
"text": "Can you click the button?",
"fallback": "Sorry, no support for buttons.",
"callback_id": "ptNotificationButtonResponse",
"color": "#3AA3E3",
"attachment_type": "default",
"actions": [
{
"name": "userResponse",
"text": "OK",
"style": "primary",
"type": "button",
"value": "ok"
}
]
}
]
}
// format for Slack
var options = {
'method' : 'post',
'contentType': 'application/json',
// Convert the JavaScript object to a JSON string.
'payload' : JSON.stringify(messageData)
};
// post to Slack
UrlFetchApp.fetch(slackUrl, options);
}
My current action URL code right now looks like this:
function doPost() {
var replyMessage = {"replace_original": true,
"response_type": "in_channel",
"text": "I see you clicked the button."
};
return ContentService.createTextOutput(JSON.stringify(replyMessage)).setMimeType(ContentService.MimeType.JSON);
}
Instead of replacing the entire original message, I'd like to replace just the buttons with something like a checkbox and confirmation message as demonstrated in the gif above.
Thanks!

Answer 1

You can only replace the complete message, not just a part.
There are two options to update the original message:
Respond to the Slack request with {"replace_original": true}
Use chat.update
If your original message was not of type ephemeral you will get a copy of the original message as part of the payload from Slack in the original_message property, which can be helpful to update the exchange the original message.
See this page in the Slack documentation as reference.