JavaScript is an interpreted programming language originally implemented as part of web browsers to enable client-side scripts that interact with users without server communication, controlling the browser, enabling asynchronous communication, and modifying displayed document content.

Today, JavaScript is the primary language for client-side programming in web browsers and is increasingly used server-side through environments like Node.js. It was designed as a prototype-based scripting language with weak and dynamic typing and first-class functions.

JavaScript supports functional programming and includes features like closures and higher-order functions, which are often unavailable in popular languages like Java and C++. It is based on ECMAScript, standardized by Ecma International under specifications ECMA-262 and ISO/IEC 16262.

JavaScript was initially developed by Brendan Eich at Netscape under the name Mocha, then renamed LiveScript, and finally JavaScript. LiveScript was the official name when it was first launched in the Netscape 2.0 browser beta version in September 1995, but it was renamed JavaScript in a joint announcement with Sun Microsystems in December 1995 when added to Netscape’s 2.0B3 version.

The renaming from LiveScript to JavaScript coincided with Netscape’s addition of Java technology support in its browser (Applets). This naming choice caused confusion, suggesting the language was based on Java, which many consider a Netscape marketing strategy to leverage Java’s popularity.

JavaScript quickly gained acceptance as the client-side scripting language for web pages. As a result, Microsoft developed a compatible dialect called JScript to avoid trademark issues. JScript included new methods to fix JavaScript’s date-related issues and was included in Internet Explorer 3.0, released in August 1996.

JavaScript and JScript are so similar that the terms are often used interchangeably, though Microsoft has identified features where JScript does not fully conform to the ECMAScript specification.

In November 1996, Netscape announced it had submitted JavaScript to Ecma International as an industry standard candidate, which led to the standardized version known as ECMAScript.