Using TypeScript and Octokit/rest.js to Comment on Pull Request or Commit

comment-on-github.ts

import { Octokit } from '@octokit/rest';
import { createAppAuth } from '@octokit/auth-app';
import { readFileSync } from 'fs';

// authorize on app level
const app = new Octokit({
    authStrategy: createAppAuth,
    auth: {
        type: "app",
        id: 12345,
        privateKey: readFileSync('app-private-key.pem')
    }
});

async function start() {

    // get the installation id
    const install = await app.apps.getRepoInstallation({
        owner: 'owner',
        repo: 'repo'
    });

    // authorize on repo level
    const appInstall = new Octokit({
        authStrategy: createAppAuth,
        auth: {
            type: "install",
            id: 12345,
            privateKey: readFileSync('app-private-key.pem')
            installationId: install.data.id
        }
    });

    // create a comment on a commit, it normally will show on on related PRs
    let result = await appInstall.repos.createCommitComment({
    // or perhaps comment on an issue/PR
    // let result = await appInstall.issues.createComment({
    //     issue_number: 42,
        owner: 'owner',
        repo: 'repo',
        commit_sha: 'sha',
        body:`### Test
This is test with markdown.
Let's see whether it works.`});

    console.log('got result: ');
    console.log(result);
}

start().then(() => console.log('done')).catch(e => { console.error(e) });