JavaScript
Overview
JavaScript is a high-level, interpreted programming language that conforms to the ECMAScript specification. It is a language that is also characterized as dynamic, weakly typed, prototype-based and multi-paradigm. JavaScript was initially created to make web pages live, introducing interactivity to the web that was previously static.
History
JavaScript was created in 1995 by Brendan Eich while he was an engineer at Netscape. The language was originally named Mocha, but was quickly renamed to LiveScript, and finally to JavaScript. The change of name from LiveScript to JavaScript roughly coincided with Netscape adding support for Java technology in its Netscape Navigator web browser. JavaScript was first introduced and deployed in the Netscape browser version 2.0B3 in December 1995.
Features
JavaScript supports imperative/procedural and structured programming styles. It has functions as first-class objects, supports object-oriented programming, and also supports functional programming. JavaScript uses syntax influenced by that of C. JavaScript copies many names and naming conventions from Java, but the two languages are otherwise unrelated and have very different semantics.
Variables
JavaScript has three kinds of variable declarations: var, let, and const. Var declarations are globally scoped or function/locally scoped while let and const are block scoped. They are all hoisted to the top of their scope. But while var variables are initialized with undefined, let and const variables are not initialized.
Data Structures
JavaScript provides several built-in data structures including Objects and Arrays. Objects in JavaScript are dynamic collections of properties, with a "hidden" property to the object's prototype. Arrays in JavaScript are dynamic, and can contain elements of different types.
Functions
Functions are first-class objects in JavaScript, meaning they can have properties and methods just like any other object. They can be stored in variables, passed as arguments to other functions, and created within and returned from functions.
Object-Oriented Programming
JavaScript supports object-oriented programming with object prototypes, rather than with classes (as in other object-oriented languages such as Java and C++). However, as of ES6 (ECMAScript 2015), JavaScript also supports class syntax, but this is mostly syntactic sugar over JavaScript's existing prototype-based inheritance.
Asynchronous Programming
JavaScript also supports asynchronous programming with callbacks, promises, and async/await syntax. This makes it possible to handle asynchronous events such as user input, file I/O, and network communication.
Usage
JavaScript is primarily used in the form of client-side JavaScript, implemented as part of a web browser in order to provide enhanced user interfaces and dynamic websites. However, its use in applications outside web pages is also significant, especially in "server-side JavaScript" applications.
Criticism and Vulnerabilities
JavaScript has been criticized for its perceived shortcomings as a programming language. These criticisms include issues related to debugging, lack of an integer type, and the complexity of the language's scoping, particularly the complex behavior of the "this" keyword and the use of prototype inheritance.
JavaScript is also often associated with a number of security vulnerabilities. Because JavaScript code can run locally in a user's browser (rather than on a remote server), the browser can serve as an attack vector for malicious activity.