ReactionAddedEvent uses non-exported sub interfaces.

[feliperyan]

Description

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• bug
• enhancement (feature request)
• question
• documentation related
• example code related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
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• I've searched for any related issues and avoided creating a duplicate issue.

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Bug Report

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Reproducible in:

package version: 3.0.0

node version: 12.3

OS version(s): MacOS 10.15.7

Steps to reproduce:

1. Define an app.event('reaction_added', async ({ event, client }) => { ... listener.
2. Try to access event.item.channel or event.item.ts

Expected result:

To be able to define which type item is = ReactionMessageItem, ReactionFileItem or ReactionFileCommentItem but these interfaces are not exported.

Actual result:

Property 'channel' does not exist on type 'ReactionMessageItem | ReactionFileItem | ReactionFileCommentItem'.
Property 'channel' does not exist on type 'ReactionFileItem'.

Full example code:

app.event('reaction_added', async ({ event, client }) => {
    console.log(`lab2 Reaction added: `, event.reaction);

    try {
        if(event.reaction === 'white_check_mark') {
              // Post message in thread of the message being reacted to
              await client.chat.postMessage({
                channel: event.item.channel,
                thread_ts: event.item.ts,
                text: `<@${event.user}> Thank you for successfully completing *lab 2* :two_hearts:`
              });
          }
    }
    catch(error) {
        console.log(error);
    }
});