JavaScript is a scripting language most often used for client-side web development. It was the originating dialect of the ECMAScript standard. It is a dynamic, weakly typed, prototype-based language with first-class functions. JavaScript was influenced by many languages and was designed to look like Java, but be easier for non-programmers to work with.

Although best known for its use in websites (as client-side JavaScript), JavaScript is also used to enable scripting access to objects embedded in other applications (see below).

JavaScript, despite the name, is essentially unrelated to the Java programming language, although both have the common C syntax, and JavaScript copies many Java names and naming conventions. The language was originally named "LiveScript" but was renamed in a co-marketing deal between Netscape and Sun, in exchange for Netscape bundling Sun's Java runtime with their then-dominant browser. The key design principles within JavaScript are inherited from the Self and Scheme programming languages.

"JavaScript" is a trademark of Sun Microsystems. It was used under license for technology invented and implemented by Netscape Communications and current entities such as the Mozilla Foundation.

History and naming

JavaScript was originally developed by Brendan Eich of Netscape under the name Mocha, which was later 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. 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.

Microsoft named its dialect of the language JScript to avoid trademark issues. JScript was first supported in Internet Explorer version 3.0, released in August 1996, and it included Y2K-compliant date functions, unlike those based on java.util.Date in JavaScript at the time. The dialects are perceived to be so similar that the terms "JavaScript" and "JScript" are often used interchangeably (including in this article). Microsoft, however, notes dozens of ways in which JScript is not ECMA compliant.

Netscape submitted JavaScript to Ecma International for standardization resulting in the standardized version named ECMAScript.

Structured programming

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. JavaScript 1.7, however, supports block-level scoping with the let keyword. Like C, JavaScript makes a distinction between expressions and statements.