What methods could be used to manage the execution of asynchronous tasks before the introduction of async/await syntax?

Before the introduction of the async/await syntax in JavaScript for managing asynchronous tasks, several main methods were used:

• Callback functions — passing a function that is called after the asynchronous operation completes:

  fs.readFile('file.txt', (err, data) => {
    if (err) throw err;
    console.log(data);
  });
  

• Promises — objects representing the result of an asynchronous operation, with .then() and .catch() methods:

  fetch(url)
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error(error));
  

• Libraries for managing asynchrony — for example, async.js, which provided convenient functions for sequential or parallel execution of tasks.

These methods allowed organizing asynchronous code, avoiding "callback hell" and improving readability before the advent of async/await.