Poder recuperar datos asíncronamente de fondo sin interferir con la visualización o comportamiento de la página
While the term "Ajax" was coined in 2005,[3] techniques for the asynchronous loading of content date back to 1996, when Internet Explorer introduced the IFrame element.[4] Microsoft's Remote Scripting, introduced in 1998, acted as a more elegant replacement for these techniques, with data being pulled in by a Java applet with which the client side could communicate using JavaScript. In 2002, Microsoft created the XMLHttpRequest object as an ActiveX control in Internet Explorer 5, and developers of Mozilla and Safari followed soon after with native versions of the object.[5][4] It did not become an official web standard until April 5, 2006, when the World Wide Web Consortium (W3C) released a specification for the object.[6]
En lugar de cargar el javascript mezclándolo con el HTML lo que se hace es cargarlo cuando se carga la página, utilizando selectores CSS
Comentar cómo funcionan los lectores de pantalla con Javascript