How does AJAX work?

If you are totally new to AJAX (which stands for Asynchronous Javascript And XML), the AJAX entry on wikipedia is a good starting point:

Like DHTML and LAMP, AJAX is not a technology in itself, but a group of technologies. AJAX uses a combination of:

  • HTML and CSS for marking up and styling information.
  • The DOM accessed with JavaScript to dynamically display and interact with the information presented.
  • A method for exchanging data asynchronously between browser and server, thereby avoiding page reloads. The XMLHttpRequest (XHR) object is usually used, but sometimes an IFrame object or a dynamically added tag is used instead.
  • A format for the data sent to the browser. Common formats include XML, pre-formatted HTML, plain text, and JavaScript Object Notation (JSON). This data could be created dynamically by some form of server-side scripting.

As you can see, from a pure technological point of view, there is nothing really new here. Most of AJAX parts were already there in 1994 (1999 for the XMLHttpRequest object). The real novelty was to use these parts together as Google did with GMail (2004) and Google Maps (2005). Actually, both sites contributed heavily to the promotion of AJAX.

A picture being worth a thousand words, below a diagram that illustrates the communication between the client and the remote server, as well as the differences between the classic and the AJAX-powered applications:

For the orange part, you can do everything by hand (with the XMLHttpRequest object) or you can use famous JavaScript libraries like jQuery, Prototype, YUI, etc to “AJAXify” the client-side of your application. Such libraries aim to hide the complexity of JavaScript development (e.g. the cross-browser compatibility), but might be overkill for a simple feature.

On the server-side, some frameworks can help too (e.g. DWR or RAJAX if you are using Java), but all you need to do is basically to expose a service that returns only the required informations to partially update the page (initially as XML/XHTML – the X in AJAX – but JSON is often preferred nowadays).

Related Posts:

  1. Cross-Origin Read Blocking (CORB)
  2. syntax error: unexpected token <
  3. Infinite Scrolling in Asp.Net MVC with jQuery / AJAX Issues
  4. ajax jquery simple get request
  5. jQuery get textarea text
  6. Response to preflight request doesn’t pass access control check
  7. jQuery AJAX cross domain
  8. Send POST data using XMLHttpRequest
  9. Set timeout for ajax (jQuery)
  10. How to generate a simple popup using jQuery
  11. What does on() in JavaScript do?
  12. jQuery AJAX submit form
  13. jQuery Ajax File Upload
  14. How can I upload files asynchronously with jQuery?
  15. Adding images to a Bootstrap Carousel with AJAX
  16. AJAX response error: net::ERR_EMPTY_RESPONSE
  17. Disable same origin policy in Chrome
  18. Access Control Request Headers, is added to header in AJAX request with jQuery
  19. React Js: Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0
  20. XMLHttpRequest status 0 (responseText is empty)
  21. Basic Ajax send/receive with node.js
  22. Execute PHP function with onclick
  23. Uncaught TypeError: Cannot read property ‘appendChild’ of null
  24. JSON.parse() not working
  25. jQuery Ajax POST example with PHP
  26. Refresh/reload the content in Div using jquery/ajax
  27. SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
  28. Scroll to bottom of div?
  29. How to manage a redirect request after a jQuery Ajax call
  30. How to allow CORS in react.js?
  31. FormData append not working
  32. Uncaught TypeError: Cannot read property ‘toLowerCase’ of undefined
  33. Download a file by jQuery.Ajax
  34. What is ‘xmlhttp.setRequestHeader();’ and in which situations is it used?
  35. “NS_ERROR_DOM_BAD_URI: Access to restricted URI denied”
  36. Ajax success function
  37. JAX post error : Refused to set unsafe header “Connection”
  38. AngularJS POST Fails: Response for preflight has invalid HTTP status code 404
  39. $http.get(…).success is not a function
  40. Adding wp_ajax to a theme outside functions.php (on specific template page)
  41. Does wp_localize_script call a Javascript Function or Simply Pass PHP Parameters to It
  42. How to make wordpress URLS google friendly for ajax driven sites?
  43. AJAX not Working with php as supposed
  44. How to make a discord bot create an invite for every server it joins?
  45. Chart.js Bar graph will not start at zero as minimum value
  46. Cannot GET / Nodejs Error
  47. Uncaught SyntaxError: Unexpected token u in JSON at position 0
  48. Setting “checked” for a checkbox with jQuery
  49. What does this symbol mean in JavaScript?
  50. Merge/flatten an array of arrays
  51. setInterval in a React app
  52. How do I declare a namespace in JavaScript?
  53. Remove duplicate values from JS array
  54. Trying to convert crmForm to Xrm.Page
  55. Encode HTML entities in JavaScript
  56. Remove last item from array
  57. Uncaught ReferenceError: define is not defined typescript
  58. jQuery count child elements
  59. javascript check for not null
  60. How do I check if an element is hidden in jQuery?
  61. Uncaught Reference Error: stLight is not defined (in Chrome only)
  62. How to get the selected radio button’s value?
  63. element.setAttribute is not a function
  64. gapi is not defined – Google sign in issue with gapi.auth2.init
  65. Remove all special characters with RegExp
  66. jQuery: Get selected element tag name
  67. Does ECMAScript 6 have a convention for abstract classes?
  68. How to check for an undefined or null variable in JavaScript?
  69. HTML anchor link – href and onclick both?
  70. How to use forEach loop correctly in angular 2?
  71. javascript push multidimensional array
  72. How can I know which radio button is selected via jQuery?
  73. jquery toggleClass not working
  74. Can WordPress be made to support websockets?
  75. How to use wp.hooks.addAction() in React JS/Gutenberg?
  76. Remove extra Google Maps script
  77. single page wordpress
  78. initial open/toggle PluginDocumentSettingPanel panel in document setting block editor gutenberg
  79. Headless WordPress: How to authenticate front end requests?
  80. AJAX issue – Uncaught SyntaxError when processing Zip File
  81. How can I get the standard WP-Editor through Javascript?
  82. class click counter save number
  83. Gutenberg select categories
  84. Performance vs plugin genrated javascript
  85. How can I load certain JavaScripts only on blog pages?
  86. Javascript for a specific wordpress page
  87. How can I leverage browser cache for minified JS or minified CS files?
  88. Close modal window after form submit [closed]
  89. Form will not popup, when clicking on the link to the form
  90. Jquery POST Ajax Return null data in wordpress
  91. internal anchor links no longer working after upgrade
  92. How do you change the text “Update failed. You are probably offline.”
  93. on change form submit variable value not updating
  94. AJAX to add to cart multiple products woocommerce
  95. How do I make a savable preview like Youtube Gutenberg block?
  96. iFrame onLoad in custom Gutenberg block
  97. The page isn’t redirecting properly was given when redirecting
  98. How To Pull Information From A Page And Input The Data In The WordPress User Database Table
  99. I keep getting Javascript error messages
  100. convertEntities() used before it is defined

Leave a Comment