What is error-first callback pattern?

javascript

const fs = require("fs");

// Error-first callback pattern
fs.readFile("file.txt", (err, data) => {
  if (err) {
    console.error("Error:", err);
    return;
  }
  console.log("Data:", data);
});

// Custom function
function getUserById(id, callback) {
  db.query("SELECT * FROM users WHERE id = ?", [id], (err, result) => {
    if (err) return callback(err);
    callback(null, result);
  });
}

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