Callback in another function

JavaScriptJunior~1 min read

A callback function can be passed simply as an argument when calling another function - since in JavaScript functions are values (first-class citizens).

Example:

javascript

function doSomething(callback) {
  console.log('Doing something...');
  callback(); // call the passed callback
}

function afterDone() {
  console.log('Done!');
}

doSomething(afterDone);

Output:

javascript

Doing something...
Done!

You can pass an anonymous callback directly at the call site:

javascript

doSomething(() => {
  console.log('Done!');
});

Summary: To pass a callback, specify it as a parameter when calling the function. And inside the receiving function, call it by name when it needs to run.

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