We are now dealing with objects that are not part of the Core JavaScript, but are provided by the environment of the web page, through its (Application Programming Interface [API]) programming interface. The tree structure of the HTML document, known as DOM (Document Object Model) is equipped with tools to handle the DOM elements and the associated events. The browser provides objects for handling the DOM, and other objects, for persistent storage (Cookies and Local Storage), for background tasks (Workers), for external requests via the HTTP protocol, the XmlHTTPRequest object, or the global function Fetch, which leads us also to present asynchronous processing.

We are at the interface between the “Core JS” embedded in the browser and the client-specific features: the APIs linked to HTML and to HTTP.

The ecosystem of the web page compounds three languages, HTML, CSS, JavaScript, and an HTTP protocol. Here is a short reminder, with comments on what may impact the JavaScript code:

– HTML dealing with the page content structure and semantics

A modern application adopts HTML5. What is fundamental to learn is the DOM. The following chapters will explain the tree structure and how to interact with it.

– CSS dealing with positioning and the cosmetics of DOM elements

A modern application adopts CSS2.1, plus some CSS3 modules (e.g. flex). What is fundamental to learn (from the JavaScript viewpoint) is the selection of the elements. A short chapter will recall these features.

– JavaScript dealing with dynamic modification and exchanges

A modern application adopts ES6. Assuming that the targeted applications are data oriented, it is useless to spend time on complying with older legacy systems. What is fundamental to learn are the notions of scope, prototype and functions as first-class objects. We will learn how this helps to correctly link the core parts and the various APIs of the window object. We will learn how to present data with graphics: plotting and animating.

– HTTP dealing with external requests that provide contents

A data-oriented application uses data repositories, served through specific APIs, and uses external scripts, provided by content delivery networks. What is fundamental to learn is how to make requests and how to manage responses. We will learn the technology AJAX and how to deal with JSON files in an asynchronous context.

The progress of standardization has been huge and all post-2015 browsers meet the standards recommended in this book.