Pass functions to other functions.
✍️ 3 exercises + code challenge in this lessonA callback is a function passed as an argument to another function, which calls it later.
You already used callbacks: the function given to addEventListener, setTimeout and array.map() is a callback.
Callbacks are the foundation of asynchronous JavaScript, but deeply nested callbacks ("callback hell") are hard to read. Promises and async/await solve that.
Mastering JavaScript Callbacks helps you write clean and reliable JavaScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
<pre id="out"></pre>
<script>
const log = (...a) => document.getElementById("out").textContent += a.join(" ") + "\n";
function calculate(a, b, operation) {
return operation(a, b);
}
log("Sum:", calculate(6, 3, (x, y) => x + y));
log("Product:", calculate(6, 3, (x, y) => x * y));
function loadUser(id, done) {
log("Loading user", id, "...");
setTimeout(() => done({ id, name: "Sara" }), 1000);
}
loadUser(7, (user) => log("Loaded:", user.name));
</script>Check what you learned in “JavaScript Callbacks”.
Pass a callback that doubles each number.
const doubled = nums.map();
What is a callback?
Write a function calculate(a, b, op) that returns op(a, b). Log calculate(6, 7, (x, y) => x * y).
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