What is a callback function in JavaScript?

A callback is a function passed as an argument to another function, which calls it later.

function process(name, callback) {
  console.log("Hello " + name);
  callback();
}

process("Robin", () => console.log("Done"));

setTimeout(() => console.log("After 1 second"), 1000);

Output:

Callbacks are used for events, timers and array methods like map. Many nested callbacks become hard to read (callback hell), and promises solve that.

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