JavaScript is a high-level, dynamic, un-typed and interpreted programming language. It has been standardized in the ECMA Script language specification. As a multi-paradigm language, JavaScript supports event-driven, functional, and imperative programming styles. It has application programming interfaces (APIs) for working with text, dates, regular expressions, standard data structures, and the Document Object Model (DOM).

The ECMAScript standard does not include any input/output (I/O), such as networking, storage, or graphics facilities. In practice, the web browser or other runtime system provides JavaScript APIs for I/O. JavaScript engines were originally used only in web browsers, but they are now core components of other software systems, most notably servers and a variety of applications. Although there are similarities between JavaScript and Java, including language name, syntax, and respective standard libraries, the two languages are distinct and differ greatly in design.

• Every major web browser has built-in web development tools, including a JavaScript debugger.

• Static program analysis tools, such as ESLint and JSLint, scan JavaScript code for conformance to a set of standards and guidelines.

• Some browsers have built-in profilers. Stand-alone profiling libraries have also been created, such as benchmark.js and jsbench.[94][95]

• Many text editors have syntax highlighting support for JavaScript code.

JavaScript is the dominant client-side language of the Web, and many websites are script-heavy. Thus transpilers have been created to convert code written in other languages, which can aid the development process.