JavaScript was originally developed by Brendan Eich of Netscape under the name Mocha, which was later renamed to LiveScript, and finally to JavaScript. [8] [9] The change of name from LiveScript to JavaScript roughly coincided with Netscape adding support for Java technology in its Netscape Navigator web browser.
In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release. [10]
The naming has caused confusion, giving the impression that the language is a spin-off of Java, and it has been characterized by many as a marketing ploy by Netscape to give JavaScript the cachet of what was then the hot new web-programming language. [11] [12] It has also been claimed that the language's name is the result of a co-marketing deal between Netscape and Sun, in exchange for Netscape bundling Sun's Java runtime with their then-dominant browser.[citation needed]
Despite the name, JavaScript is essentially unrelated to the Java programming language even though the two do have superficial similarities. Both languages use syntaxes influenced by that of C syntax, and JavaScript copies many Java names and naming conventions. However, the key design principles within JavaScript are taken from the Self and Scheme programming languages. [13]
JavaScript was first deployed in the Netscape browser version 2.0B3 in December 1995.
Due to the widespread success of JavaScript as a client-side scripting language for web pages, Microsoft developed a compatible dialect of the language, naming it JScript to avoid trademark issues. JScript added new date methods to fix the non-Y2K-friendly methods in JavaScript, which were based on java.util.Date.[7] JScript was included in Internet Explorer 3.0, released in August 1996. The dialects are perceived to be so similar that the terms "JavaScript" and "JScript" are often used interchangeably. (Microsoft, however, notes dozens of ways in which JScript is not ECMA-compliant.[14])
In November, 1996 Netscape announced that it had submitted JavaScript to Ecma International for consideration as an industry standard, and subsequent work resulted in the standardized version named ECMAScript.[15]
"JavaScript" is a trademark of Sun Microsystems. It is used under license for technology invented and implemented by Netscape Communications and current entities such as the Mozilla Foundation.[16]
JavaScript has become one of the most popular programming languages on the web. Initially, however, many professional programmers denigrated the language because its target audience was web authors and other such "amateurs", among other reasons.[17] The advent of Ajax returned JavaScript to the spotlight and brought more professional programming attention. The result was a proliferation of comprehensive frameworks and libraries, improved JavaScript programming practices, and increased usage of JavaScript outside of web browsers, as seen by the proliferation of server-side JavaScript platforms.
In January 2009 the CommonJS project was founded with the goal of specifying a common standard library mainly for JavaScript development outside the browser.[18]
Features
The following features are common to all conforming ECMAScript implementations, unless explicitly specified otherwise.
Imperative and structured
JavaScript supports all the structured programming syntax in C (e.g., if statements, while loops, switch statements, etc.). One partial exception is scoping: C-style block-level scoping is not supported (instead, JavaScript has function-level scoping). JavaScript 1.7, however, supports block-level scoping with the let keyword. Like C, JavaScript makes a distinction between expressions and statements. One syntactic difference from C is automatic semicolon insertion, in which the semicolons that terminate statements can be omitted.[19]
Dynamic
dynamic typing
As in most scripting languages, types are associated with values, not variables. For example, a variable x could be bound to a number, then later rebound to a string. JavaScript supports various ways to test the type of an object, including duck typing.[20]
object based
JavaScript is almost entirely object-based. JavaScript objects are associative arrays, augmented with prototypes (see below). Object property names are string keys: obj.x = 10 and obj["x"] = 10 are equivalent, the dot notation being syntactic sugar. Properties and their values can be added, changed, or deleted at run-time. Most properties of an object (and those on its prototype inheritance chain) can be enumerated using a for...in loop. JavaScript has a small number of built-in objects such as Function and Date.
run-time evaluation
JavaScript includes an eval function that can execute statements provided as strings at run-time.
Functional
first-class functions
Functions are first-class; they are objects themselves. As such, they have properties and can be passed around and interacted with like any other object.
inner functions and closures
Inner functions (functions defined within other functions) are created each time the outer function is invoked, and variables of the outer functions for that invocation continue to exist as long as the inner functions still exist, even after that invocation is finished (e.g. if the inner function was returned, it still has access to the outer function's variables) — this is the mechanism behind closures within JavaScript.
Prototype-based
prototypes
JavaScript uses prototypes instead of classes for inheritance. It is possible to simulate many class-based features with prototypes in JavaScript.
functions as object constructors
Functions double as object constructors along with their typical role. Prefixing a function call with new creates a new object and calls that function with its local this keyword bound to that object for that invocation. The constructor's prototype property determines the object used for the new object's internal prototype. JavaScript's built-in constructors, such as Array, also have prototypes that can be modified.
functions as methods
Unlike many object-oriented languages, there is no distinction between a function definition and a method definition. Rather, the distinction occurs during function calling; a function can be called as a method. When a function is called as a method of an object, the function's local this keyword is bound to that object for that invocation.
Miscellaneous
run-time environment
JavaScript typically relies on a run-time environment (e.g. in a web browser) to provide objects and methods by which scripts can interact with "the outside world". In fact, it relies on the environment to provide the ability to include/import scripts (e.g. HTML
JavaScript
