In computer programming, a request is an operation that is made to a computer system or server to retrieve or update information. There are two main types of requests: synchronous and asynchronous.

A synchronous request is a request that blocks, or stops, the execution of a program until it has received a response. This means that the program will wait for the request to be completed before moving on to the next line of code. Synchronous requests are simple and easy to use, but they can be slower and less efficient because they require the program to pause and wait for the response.

On the other hand, an asynchronous request is a request that does not block the execution of a program. This means that the program can continue to run while the request is being processed in the background. Asynchronous requests are faster and more efficient because they allow the program to continue running while the request is being processed.

So, when should you use synchronous requests and when should you use asynchronous requests? It depends on the specific needs of your program. If you need to retrieve a small amount of data that is not time-sensitive, a synchronous request may be sufficient. However, if you are dealing with large amounts of data or need to make several requests in quick succession, an asynchronous request may be a better choice.

In general, asynchronous requests are preferred for performance-critical applications because they allow the program to continue running while the request is being processed. However, it is important to keep in mind that asynchronous requests can be more complex to implement and may require more code.

Examples for asynchronous in JavaScript are async and await keywords are used to work with asynchronous code.

The async keyword is used to declare a function as asynchronous. Asynchronous functions are functions that return a promise and can be awaited. Here is an example of an asynchronous function:

async function fetchData() {
  const response = await fetch('https://api.example.com/data');
  const data = await response.json();
  return data;
}

The await keyword is used to wait for a promise to be resolved. It can only be used inside an async function. The await keyword allows you to write asynchronous code in a synchronous-like style, making it easier to read and understand.

Here is an example of how await can be used to retrieve data from an API:

async function getData() {
  const data = await fetchData();
  console.log(data);
}

In this example, the getData function is an asynchronous function that calls the fetchData function and waits for the promise to be resolved before logging the data to the console.

The choice between synchronous and asynchronous requests will depend on the specific needs of your program and the trade-offs you are willing to make between performance and simplicity.