read-file-with-callback.ts

import { readFile } from 'node:fs';

const readFileCallback = (err: Error | null, data: string | Buffer) => {
  if (err) {
    console.log(err);
    return;
  }
  
  // process data ...
  console.log(data.length);
}

const main = () => {
  readFile('/tmp/data', readFileCallback);
}

main();