As the name implies, XMLHttpRequest is the object that can make http request from web page. It is usually used to get access to remote page (or any page other than current html) and manipulate it.


NOTE : In this note, I am trying to use chatGPT in a little bit different way. Instead of asking chatGPT to write a specific code that I requested, I asked chatGPT about generic questions about Javascript. I just asked some generic questions and copied the answers in this note and will keep adding my persona comments afterwords.


NOTE : What is the point of just doing copy and paste of what chatGPT writes out. You can ask the same question directly into chatGPT. There are a couple of reasons as below.

  • After some time, I often forget my own question.
  • In many cases, chatGPT replies a little bit differently even with the same question. Some replies are pretty satisfactory but some are not. So I learned that it would be good idea to copy and store it somewhere else whenever you get qood answers.
  • Purely for curiosity. I want to observe myself about how much I can collobrate with chatGPT in various different way (e.g, in writing specific code or in general technical conversation)




Properties of XMLHttpRequest


  • onreadystatechange: A callback function that is called every time the readyState property changes.
  • readyState: An integer that indicates the state of the request. Possible values are:
    • 0: Uninitialized
    • 1: Loading
    • 2: Loaded
    • 3: Interactive
    • 4: Completed
  • responseText: A string that contains the response from the server as plain text.
  • responseXML: A Document Object Model (DOM) object that contains the response from the server as an XML document.
  • status: An integer that indicates the HTTP status code of the response. Common status codes include 200 (OK), 404 (Not Found), and 500 (Internal Server Error).
  • statusText: A string that describes the HTTP status code of the response.
  • timeout: An integer that specifies the number of milliseconds a request can take before automatically being terminated.
  • withCredentials: A Boolean value that indicates whether or not to include user credentials in the request




Methods of XMLHttpRequest


  • open(method, url, async, username, password): Initializes a request. The method argument specifies the type of request (e.g. GET or POST), the URL argument specifies the URL to be requested, and the async argument specifies whether the request should be asynchronous (true) or synchronous (false). The username and password arguments are optional and are used for authentication.
  • send(data): Sends the request to the server. The data argument is optional and can be used to send data with the request.
  • abort(): Cancels the current request.
  • getAllResponseHeaders(): Returns a string containing all of the response headers separated by CRLF.
  • getResponseHeader(headerName): Returns the value of the specified response header.
  • setRequestHeader(header, value): Sets a request header to be used in the request.
  • overrideMimeType(mime): Overrides the MIME type returned by the server.
  • addEventListener(type, listener, useCapture): Adds an event listener to the XMLHttpRequest object.
  • removeEventListener(type, listener, useCapture): Removes an event listener from the XMLHttpRequest object.




Challenges and Cautions


I personally came across a lot of issues when I use this object in the script. I don't think most of the issues are based on the problem of HMLHttpRequest object itself. In most case, it is related to various factors outside of the object as listed below.

  • Browser compatibility: Support for the XMLHttpRequest object varies among browsers. Some older browsers may not support the latest features, or may have limited support for the object. You may need to use a library such as jQuery or Axios to ensure compatibility across all browsers.
  • Security restrictions: The XMLHttpRequest object is subject to the same origin policy, which means that it can only make requests to the same domain that the page was loaded from. Requests to other domains will be blocked for security reasons.
  • Asynchronous behavior: Requests made with the XMLHttpRequest object are asynchronous by default, which means that they do not block other code from running while the request is being processed. This can be a challenge if you need to make multiple requests in a specific order, or if you need to wait for a response before executing other code.
  • Error handling: It can be challenging to handle errors that occur during an XMLHttpRequest request, as they are not automatically caught by the JavaScript error handling mechanism. You will need to check the status and statusText properties of the XMLHttpRequest object and handle any errors manually.
  • Cross-site scripting (XSS): If your application is not properly validated, an attacker could inject malicious code into your page via the response from the server. You should always validate the data returned by the server before using it in your page to prevent XSS attacks.