Asynchronous Programming

Asynchronous (async) programming is a way of writing code so that a slow operation, such as an HTTP request, file read or database query, runs in the background while the program keeps doing other work. The result arrives later through a callback, a promise or an await expression.

Why it matters

Servers and user interfaces spend most of their time waiting. If every wait blocks, a web server handles one request at a time and an app freezes. Async code lets one thread juggle thousands of waiting operations, which is how Node.js and many modern Python servers scale.

Example

async function check(urls) {
  const results = await Promise.all(
    urls.map(u => fetch(u).then(r => r.status))
  );
  return results;   // all requests ran at the same time
}

Fetching three URLs sequentially might take 900 ms if each takes 300 ms; running them concurrently takes about 300 ms.

Common mistakes

• Forgetting await, so you work with an unfinished promise instead of its result.
• Running a CPU-heavy loop inside async code, which blocks everything else.
• Not handling errors from rejected promises, which then fail silently.

Related

• Thread
• Race condition
• Exception
• Webhook

यह पेज सामान्य जानकारी है, जिसे हमारी संपादकीय टीम ने लिखा है और दस्तावेज़ीकरण बदलने पर अपडेट किया जाता है। सर्वर और प्रदाता अलग-अलग होते हैं, इसलिए बदलाव पहले सुरक्षित तरीके से जाँचें। देखें: संपादकीय नीति और अस्वीकरण.