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JavaScript in Detail: From Beginner to Advanced

Asynchronicity in JavaScript

Explore JavaScript's asynchronous programming by understanding how callbacks work with the event loop and callback queue. Learn to handle non-blocking code flow using functions like setTimeout, and grasp how JavaScript environments manage asynchronous events for efficient execution.

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Background

JavaScript supports asynchronous programming. However, writing asynchronous programs is tricky if you don’t have knowledge of the blocking code and JavaScript. Let’s dive deeper into how asynchronicity is engineered in the language.

Callback functions

To leverage asynchronous functions in JavaScript, design callback functions. Callback functions are invoked as soon as the blocking function finishes. Let’s revisit an example.

Node.js
function complete(){
  console.log("function completed!");
  return;
}
setTimeout(complete, 2000.0); // 2000 = 2 seconds of idle time

Above, the complete function acts as the callback function for setTimeout function. When setTimeout function ends, it ...