𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗦𝘆𝗻𝗰 𝘃𝘀 𝗔𝘀𝘆𝗻𝗰

𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁 𝗦𝘆𝗻𝗰 𝘃𝘀 𝗔𝘀𝘆𝗻𝗰

JavaScript runs code one line at a time. This is synchronous behavior. The engine finishes one task before it starts the next.

JavaScript has one main thread. It does one task at a time.

Some tasks take time.

• Fetching data from a server.
• Waiting for a timer.
• Reading local storage.

If JavaScript waits for these tasks, your page freezes. Buttons stop responding. The user experience suffers.

Asynchronous behavior solves this. JavaScript starts a long task. It continues running the rest of your code. It does not block the program.

Look at setTimeout.

1. Log Hi.
2. Set timer for 2 seconds.
3. Log Bye.

The output is: Hi Bye Run after 2 seconds

JavaScript does not wait for the timer. It prints Bye first.

Even a 0 second timer runs after the main code. The browser handles these tasks. JavaScript gets a notification when the task ends.

Main points:

• Synchronous: Code runs in order.
• Single-threaded: One task at a time.
• Asynchronous: Long tasks run in the background.
• Result: Your page stays responsive.

Source: https://dev.to/tejas_khanolkar_473f3ed1a/synchronous-and-asynchronous-behavior-of-javascript-2cp1