---
title: AJAX Request
description: "> The XMLHttpRequest object is used to exchange data with a server. ## Send a Request To a Server To send a request to a server, we use the open() and send() methods of the `XMLHttpRequest` object: `xhttp.open(\"GET\", \"ajax_info.txt\", true); xhttp.send();` |…"
url: "https://apprentice.mn/docs/ajax-request/"
updated: "2021-05-19"
category: Javascript
---

# AJAX Request

> The XMLHttpRequest object is used to exchange data with a server.

## Send a Request To a Server

To send a request to a server, we use the open() and send() methods of the `XMLHttpRequest` object:

             `xhttp.open("GET", "ajax_info.txt", true);
xhttp.send();`

| Method | Description |
| --- | --- |
| open(*method, url, async*) | Specifies the type of request *method*: the type of request: GET or POST *url*: the server (file) location *async*: true (asynchronous) or false (synchronous) |
| send() | Sends the request to the server (used for GET) |
| send(*string*) | Sends the request to the server (used for POST) |

## GET or POST?

`GET` is simpler and faster than `POST`, and can be used in most cases.

However, always use POST requests when:

- A cached file is not an option (update a file or database on the server).
- Sending a large amount of data to the server (POST has no size limitations).
- Sending user input (which can contain unknown characters), POST is more robust and secure than GET.

## GET Requests

A simple `GET` request:

### Example

      `xhttp.open("GET", "demo_get.asp", true);
xhttp.send();`

If you want to send information with the `GET` method, add the information to the URL:

### Example

      `xhttp.open("GET", "demo_get2.asp?fname=Henry&lname=Ford", true);
xhttp.send();`

## POST Requests

A simple `POST` request:

### Example

              `xhttp.open("POST", "demo_post.asp", true);
xhttp.send();`

To POST data like an HTML form, add an HTTP header with `setRequestHeader()`. Specify the data you want to send in the `send()` method:

### Example

      `xhttp.open("POST", "ajax_test.asp", true);
xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhttp.send("fname=Henry&lname=Ford");`

| Method | Description |
| --- | --- |
| setRequestHeader(*header, value*) | Adds HTTP headers to the request *header*: specifies the header name *value*: specifies the header value |

 

## The url – A File On a Server

The url parameter of the `open()` method, is an address to a file on a server:

             `xhttp.open("GET", "ajax_test.asp", true);`

The file can be any kind of file, like .txt and .xml, or server scripting files like .asp and .php (which can perform actions on the server before sending the response back).

## Asynchronous – True or False?

Server requests should be sent asynchronously.

The async parameter of the open() method should be set to true:

             `xhttp.open("GET", "ajax_test.asp", true);`

y sending asynchronously, the JavaScript does not have to wait for the server response, but can instead:

- execute other scripts while waiting for server response
- deal with the response after the response is ready

## The onreadystatechange Property

With the `XMLHttpRequest` object you can define a function to be executed when the request receives an answer.

The function is defined in the `onreadystatechange` property of the `XMLHttpRequest` object:

### Example

      `xhttp.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {
    document.getElementById("demo").innerHTML = this.responseText;
  }
};
xhttp.open("GET", "ajax_info.txt", true);
xhttp.send();`

You will learn more about `onreadystatechange` in a later chapter.

## Synchronous Request

To execute a synchronous request, change the third parameter in the `open()` method to `false`:

 xhttp.open(“GET”, “ajax_info.txt”, false);

Sometimes async = false are used for quick testing. You will also find synchronous requests in older JavaScript code.

Since the code will wait for server completion, there is no need for an `onreadystatechange` function:

### Example

      `xhttp.open("GET", "ajax_info.txt", false);
xhttp.send();
document.getElementById("demo").innerHTML = xhttp.responseText;`

Synchronous XMLHttpRequest (async = false) is not recommended because the JavaScript will stop executing until the server response is ready. If the server is busy or slow, the application will hang or stop.

Synchronous XMLHttpRequest is in the process of being removed from the web standard, but this process can take many years.

Modern developer tools are encouraged to warn about using synchronous requests and may throw an InvalidAccessError exception when it occurs.

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