The XMLHttpRequest JavaScript Object | Qt Qml | Qt 6.12.0
Description: Object for sending requests to a server.

- Qt 6.12
- Qt Qml
- The QML Reference
- Integrating QML and JavaScript
- JavaScript Host Environment
- The XMLHttpRequest JavaScript Object
- Qt 6.12.0 Reference Documentation

The Date JavaScript Object ◦ List of JavaScript Objects and Functions

# The XMLHttpRequest JavaScript Object

The `XMLHttpRequest` object allows scripts to perform HTTP client functionality, such as submitting form data or loading data asynchronously from a server.

The `XMLHttpRequest` API is a partial implementation of the W3C XHR Level 1 standard with the following exception:

- It does not enforce the same origin policy.

## Sending requests

Use the following steps to send a request using the `XMLHttpRequest` API:

1. Create a `XMLHttpRequest` object.
2. Assign a callback function to the onreadystatechange signal handler.
3. Call open() with the appropriate HTTP method and URL to request.
4. Call send()

The callback function handles the HTTP response for a request. It's a good practice to check if the readyState is `DONE` in the handler, before you use one of the following methods to read the response:

- response
- responseText
- responseXML

The following example demonstrates how to send a request and read the response:

     import QtQuick
     import QtQuick.Layouts
     import QtQuick.Controls
     import "request.js" as XHR

     ApplicationWindow {
           width: 640
           height: 640
           visible: true

           ColumnLayout {
                anchors.fill: parent

                RowLayout {
                    Layout.fillWidth: true

                    TextField {
                        id: urlTextField
                        text: "https://www.example.com/index.html"
                        Layout.fillWidth: true
                    }
                    Button {
                        text: qsTr("Send!")
                        onClicked: XHR.sendRequest(urlTextField.text, function(response) {
                            statusTextField.text = response.status;
                            let isPlainText = response.contentType.length === 0

                            contentTypeTextField.text = isPlainText ? "text" : response.contentType;

                            if (isPlainText)
                                contentTextArea.text = response.content;
                        });
                    }
                }

                GridLayout {
                    columns: 2

                    Layout.fillWidth: true

                    Label {
                        text: qsTr("Status code")

                        Layout.fillWidth: true
                    }
                    Label {
                        text: qsTr("Response type")

                        Layout.fillWidth: true
                    }
                    TextField {
                         id: statusTextField

                         Layout.fillWidth: true
                    }
                    TextField {
                         id: contentTypeTextField

                         Layout.fillWidth: true
                    }
                }
                Flickable {
                    clip: true
                    contentWidth: contentTextArea.width
                    contentHeight: contentTextArea.height
                    Text {
                         id: contentTextArea
                    }

                    Layout.fillWidth: true
                    Layout.fillHeight: true
                    ScrollBar.vertical: ScrollBar {}
                    ScrollBar.horizontal: ScrollBar {}
                }
           }
     }

The earlier snippet connects the button's clicked signal to an external `sendRequest` function. A resource URL is passed as the first argument, and a callback function to handle UI updates is passed as the second. The `sendRequest` function, which exists in an external `request.js` file, can be implemented like this:

     function sendRequest(url, callback)
     {
         let request = new XMLHttpRequest();

         request.onreadystatechange = function() {
             if (request.readyState === XMLHttpRequest.DONE) {
                 let response = {
                     status : request.status,
                     headers : request.getAllResponseHeaders(),
                     contentType : request.responseType,
                     content : request.response
                 };

                 callback(response);
             }
         }

         request.open("GET", url);
         request.send();
     }

The earlier snippet follows the four simple steps mentioned at the beginning. It instantiates the `XMLHttpRequest` object first, and assigns a callback function to handle the response. It also calls open() with an HTTP method and URL, before it sends the request to the server. Notice that the second argument to `sendRequest` is called at the end of onreadystatechange, in order to handle UI updates based on the HTTP response.

Set the `QML_XHR_DUMP` environment variable to `1` if you want to debug a request. This will log the following information:

- Method type (GET or POST), URL, and body of sent requests.
- URL and body of responses received.
- Network error, if any.

## Accessing local files

By default, you cannot use the `XMLHttpRequest` object to read files from your local file system. If you wish to use this feature to access local files, you can set the following environment variables to `1`.

- QML_XHR_ALLOW_FILE_READ
- QML_XHR_ALLOW_FILE_WRITE

Warning: Use this feature only if you know that the application runs trusted QML and JavaScript code.

## responseXML document

The `responseXML` XML DOM tree currently supported by QML is a reduced subset of the DOM Level 3 Core API supported in a web browser. The following objects and properties are supported by the QML implementation:

Node | Document | Element | Attr | CharacterData | Text
--- | --- | --- | --- | --- | ---
nodeName nodeValue nodeType parentNode childNodes firstChild lastChild previousSibling nextSibling attributes | xmlVersion xmlEncoding xmlStandalone documentElement | tagName | name value ownerElement | data length | isElementContentWhitespace wholeText

## void XMLHttpRequest::abort()

Cancels the current request.

It changes the readyState property to be `XMLHttpRequest.UNSENT` and emits the `readystatechange` signal.

## string XMLHttpRequest::getAllResponseHeaders()

Returns a `String` of headers received from the last response.

The following is an example response header:

     content-encoding: gzip
     content-type: text/html; charset=UTF-8
     date: Mon, 06 Feb 2023 09:00:08 GMT
     expires: Mon, 13 Feb 2023 09:00:08 GMT
     last-modified: Thu, 17 Oct 2019 07:18:26 GMT

## string XMLHttpRequest::getResponseHeader(headerName)

Returns either the headerName value from the last response, or an empty `String`, if the headerName is missing.

## void XMLHttpRequest::open(method, url, async)

Specify the HTTP method you want the request to use, as well as the url you wish to request. You should make sure to always call this function before send(). An optional third parameter async can be used to decide whether the request should be asynchronous or not. The default value is `true`.

Emits the `readystatechange` signal, which calls the onreadystatechange handler with the readyState property set to `XMLHttpRequest.OPENED`.

## void XMLHttpRequest::send(data)

Sends the request to the server. You can use the optional argument data to add extra data to the body of the request. This can be useful for POST requests, where you typically want the request to contain extra data.

The readyState property is updated once a response has been received from the server, and while the response is being processed. It will first be set to `HEADERS_RECEIVED`, then to `LOADING`, and finally `DONE`, once the response has been fully processed. The `readystatechange` signal is emitted every time readyState is updated.

## void XMLHttpRequest::setRequestHeader(header, value)

Adds a new header to the next request you wish to send. This is a key-value pair, which has the name header and the corresponding value.

## void XMLHttpRequest::overrideMimeType(mime)

Forces the `XMLHttpRequest` to interpret the data received in the next HTTP response, as if it had the MIME type mime, rather than the one provided by the server.

## function XMLHttpRequest::onreadystatechange

Choose a callback function you want to get invoked whenever the readyState of the `XMLHttpRequest` object changes.

## enumeration XMLHttpRequest::readyState

Indicates the current state of the `XMLHttpRequest` object.

The value can be one of the following:

Constant | Description
--- | ---
`XMLHttpRequest.UNSENT` | The request is not initialized, which is the state before calling open().
`XMLHttpRequest.OPENED` | The request is initialized, meaning open() was previously called, but no further progress.
`XMLHttpRequest.HEADERS_RECEIVED` | Received a reply from the sever, but the request is not fully processed yet.
`XMLHttpRequest.LOADING` | Downloading data from the server.
`XMLHttpRequest.DONE` | Finished processing the request.

## string XMLHttpRequest::responseURL

Returns the url that was used to retrieve the response data, after any redirects have occurred.

## string XMLHttpRequest::responseText

Returns a `String` containing the data received from the last response.

## var XMLHttpRequest::responseXML

Returns either a `Document`, or `null`, if the response content cannot be parsed as XML or HTML. See the responseXML document section for more information.

## var XMLHttpRequest::response

Returns either a `String`, an `ArrayBuffer`, or a `Document`, depending on the responseType of the last request.

## string XMLHttpRequest::responseType

Returns a `String` describing the content type of the last response received.

- If the response type is "text" or an empty `String`, the response content is a UTF-16 encoded `String`.
- If the response type is "arraybuffer", it means that the response content is an `ArrayBuffer` containing binary data.
- If the response type is "json", the response content should be a JSON `Document`.
- If the response type is "document", it means that the response content is an XML `Document`, which can be safely read with the responseXML property.

## int XMLHttpRequest::status

Returns the status code for the last response received.

## string XMLHttpRequest::statusText

Returns a `String` that has the status message associated with the status code for the last response received.

See also getResponseHeader(), getAllResponseHeaders(), readyState, onreadystatechange, responseXML, responseText, responseType, response, statusText, and status.

The Date JavaScript Object ◦ List of JavaScript Objects and Functions