JavaScript scripting client language

The purpose and use of javascript
general information

JavaScript is a relatively simple object-oriented language designed to create small client and server applications for the Internet. Programs written in JavaScript are included in the HTML documents and distributed with them. Browsers (browsers - from the English browser) such as Netscape Navigator and Microsoft Internet Explorer recognize embedded program (script-codes) embedded in the text of the document and execute them. Thus, JavaScript is an interpreted programming language. Examples of JavaScript programs are programs that validate user input or perform some actions when opening or closing a document. Such programs can react to user actions - by pressing the "mouse" buttons, entering data in a screen form, or moving the "mouse" around the page. Moreover, JavaScript programs can control the browser itself and the attributes of the document.

The JavaScript language, being syntactically similar to the Java language, with the exception of the object model, at the same time does not possess such properties as static data types and strong typing. In JavaScript, unlike Java, the concept of classes is not the basis of the syntactic constructs of a language. Such a foundation is a small set of predefined data types supported by an executable system: numeric, Boolean, and string; functions that can be both independent and object methods (in JavaScript terminology, a method is nothing but a function / subroutine); an object model with a large set of predefined objects with its properties and methods, as well as rules for setting new objects in the user program.

No additional tools are required to create JavaScript programs — only a browser that supports the corresponding version of JavaScript and a text editor that allows you to create HTML documents is needed. Since the JavaScript program is embedded directly in the text of the HTML document, you can immediately see the results of your work while the browser is viewing the document and make changes if necessary.

The name "JavaScript" is proprietary to Netscape. The implementation of the language implemented by Microsoft developers is officially called Jscript. JScript versions are compatible (if not completely accurate, not completely) with the corresponding versions of JavaScript, i.e. JavaScript is a subset of the JScript language.

JavaScript is standardized by ECMA (European Computer Manufacturers Association). Relevant standards are called ECMA-262 and ISO-16262. These standards define ECMAScript, which is roughly equivalent to JavaScript 1.1. Note that not all JavaScript implementations fully comply with the ECMA standard today. In this course, we will use the name JavaScript in all cases.