JS Advanced Programming Third Edition--javascript introduction

　A brief history of JavaScript

JavaScript was released in 1995 by Netscape (Netscape), the first major goal was to deal with some of the input validation operations previously handled by the server-side language in order to improve the user experience, and then slowly evolve into a powerful programming language. The author suggests that the key to understanding and mastering JavaScript is to understand its nature, history and limitations.

　　JavaScript implementation

A complete JavaScript implementation = Core (ECMAScript) + Document Object Model (DOM) + Browser object Model (BOM).

1. ECMAScript: the ECMAScript defined by ECMA-262 has no dependency on the Web browser. In fact, the language itself contains both input and output definitions, and ECMA-262 defines only the basis of the language, on which a more complete scripting language can be built. It is an international WEB standard for scripting languages in the hosting environment. Extension: ECMAScript is a scripting language that is standardized by the European Computer Manufacturers Association (ECMA) through ECMA-262. This language is widely used on the World Wide Web, and it is often referred to as JavaScript or JScript, but the latter is actually an extension of the ECMA-262 standard. The relationship between ECMAScript and JavaScript is that the former is the specification of the latter, which is an implementation of the former.

2. Document Object Model: is an application programming interface for XML but extended for HMTL. The DOM maps the entire page into a multi-tiered node structure. Each component of an HTML or XML page is a node of a certain type, and these nodes contain different types of data. With DOM developers, you can modify the appearance and content of a Web page without reloading it for the first time. Where the Document Object model is divided into three levels:

The DOM1 level consists of two modules, the DOM core and Dom HTML, the core of which is how to map an XML-based document structure to simplify access and manipulation of any part of the document, and the DOM HTML module expands on the DOM core, adding objects and methods for HTML.

DOM2 level in the original DOM on the basis of the expansion of the mouse and user interface events, scope, traverse (iterative DOM document method) and other subdivision modules, and through the object interface to add support for CSS, DOM2 level introduced a new module, but also gives a lot of new types and new interface definition.

The DOM3 scale further expands the DOM, introduces methods for loading and saving documents in a uniform manner, adds methods for validating documents, and extends the DOM core.

3. Browser object Model (Browser): provides a content-independent object structure that can interact with the browser window. A BOM consists of multiple objects, which represent the window object of the browser windows as the top-level object of the BOM, and the other objects are child objects of that object. The browser object Model (BOM) gives JavaScript the ability to "talk" to the browser.

　　section of this chapter

JavaScript is a scripting language designed for interacting with Web pages, consisting of three parts: ecmascrpt (ECMA-262 definition, providing core language functionality), Document Object Model (provides methods and interfaces for accessing and manipulating Web page content) The browser object model (provides methods and interfaces for interacting with the browser).

A brief history of JavaScript

JS Advanced Programming Third Edition--javascript introduction