Basic Callbacks in JavaScript
From the Async JavaScript cheat sheet · Callbacks · verified Jul 2026
Basic Callbacks
Traditional pattern for handling asynchronous operations with callback functions
javascript
// Simple callback
function getData(callback) {
setTimeout(() => {
callback('Data loaded');
}, 1000);
}
getData(result => console.log(result));
// Error-first callback (Node.js pattern)
function readFile(path, callback) {
fs.readFile(path, (err, data) => {
if (err) callback(err, null);
else callback(null, data);
});
}💡 Callbacks are functions passed as arguments to be executed later
⚠️ Can lead to "callback hell" with deep nesting
📌 Error-first convention: first parameter is for errors
🔄 Still used in many Node.js APIs and older libraries