What is javascript

Javascript is a lightweight, interpreted or just-in-time compiled programming language with function priority. It is a high-level scripting language for the Internet. JavaScript has been widely used in web application development, and is often used to add various dynamic functions to web pages to provide users with smoother and more beautiful browsing effects.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

JavaScript ("JS" for short) is a lightweight, interpreted or just-in-time compiled programming language with function priority. Although it is famous as a scripting language for developing Web pages, it is also used in many non-browser environments. JavaScript is based on prototype programming, a multi-paradigm dynamic scripting language, and supports object-oriented, imperative, declarative, and functional programming paradigm.

JavaScript is a web-oriented programming language that is supported by all web browsers. It is one of the most widely used script programming languages ​​and is also a basic tool that must be mastered for web design and web applications. It has been widely used in web application development and is often used to add various dynamic functions to web pages to provide users with smoother and more beautiful browsing effects.

JavaScript History

In February 1995, Netscape released the Netscape Navigator 2 browser and provided a development tool-LiveScript for free in this browser. Because Java was more popular at the time, Netscape renamed LiveScript to JavaScript, which was also the original JavaScript 1.0 version.

Due to the popularity of JavaScript 1.0, Netscape released JavaScript 1.1 in Netscape Navigator 3. Soon, Microsoft also added scripting capabilities to Internet Explorer 3. To avoid any dispute with Netscape's JavaScript, Microsoft named it JScript.

In 1997, the European Computer Manufacturers Association (ECMA) developed a scripting language standard - ECMA-262 based on JavaScript 1.1, and named it ECMAScript.

In 1998, the International Organization for Standardization and the International Electrotechnical Commission (ISO/IEC) adopted the ECMAScript standard (i.e., ISO/IEC-16262). Since then, browser manufacturers have used ECMAScript as the standard for their respective JavaScript implementations. JavaScript has officially moved from fragmentation to standardization.

JavaScript Composition

ECMAScript is the standard for JavaScript, but it is not the same as JavaScript, nor is it the only standardized specification.

In fact, a complete JavaScript implementation consists of the following 3 different parts:

• Core (ECMAScript): The core part of the language.

• Document Object Model (DOM): Web document operation standard.

• Browser Object Model (BOM): The basis for client and browser window operations.

Web browsers are just one of the host environments for ECMAScript implementations. The host environment not only provides basic ECMAScript implementation, but also provides various extended functions.

The Document Object Model is the application programming interface (API) of HTML. DOM maps the entire document into a tree node structure to facilitate quick access and operation by JavaScript scripts.

IE3.0 and Netscape Navigator 3.0 provide a new feature, the BOM (Browser Object Model). BOM can be used to access and operate browser windows, such as moving windows, access history, dynamic navigation, etc. Unlike DOM, BOM is only a part of JavaScript and does not form a normative standard, but it is supported by all browsers by default.

JavaScript script language has the following characteristics:

• Script language. JavaScript is an interpreted scripting language. Languages ​​such as C and C are compiled first and then executed, while JavaScript is interpreted line by line during the running of the program.

• Object based. JavaScript is an object-based scripting language that can not only create objects but also use existing objects.

• Simple. The JavaScript language uses weakly typed variable types and does not impose strict requirements on the data types used. It is a scripting language based on Java's basic statements and controls, and its design is simple and compact.

• Dynamic. JavaScript is an event-driven scripting language that can respond to user input without going through a Web server. When visiting a web page, JavaScript can directly respond to these events when the mouse is clicked, moved up or down, or moved in the window.

• Cross-platform. The JavaScript scripting language does not depend on the operating system and only requires browser support. Therefore, after writing a JavaScript script, it can be brought to any machine for use, provided that the browser on the machine supports the JavaScript scripting language. JavaScript has been supported by most browsers. Unlike server-side scripting languages, such as PHP and ASP, JavaScript is mainly used as a client-side scripting language to run on the user's browser and does not require server support. Therefore, in the early days, programmers preferred JavaScript to reduce the burden on the server, but at the same time it also brought about another problem, security.

[Recommended learning: javascript advanced tutorial]

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