Asynchronous

Synchronous

• JavaScript executes code in sequence. If some code takes long time it will wait for it.

Asynchronous

• JavaScript will execute some code in asynchronous fashion. It will call the code and won't wait for its completion and proceed with execution of the other code.
• Many functions are provided by JavaScript host environments that allow you to schedule asynchronous actions. In other words, actions that we initiate now, but they finish later.
• Examples of asynchronous
  • timeout function
  • loading script dynamically
  • sending http request using XHR, fetch
• You can handle the result asynchronous code using
  • Callbacks
  • Promises
  • Async Await

Timer

• Timer codes are executed asynchronously
• setTimeout Sets a timer which executes a function or specified piece of code once the timer expires.
• setInterval: Repeatedly calls a function or executes a code snippet, with a fixed time delay between each call.