ES4

ECMAScript 4, commonly referred to as ES4, was a proposed revision of the JavaScript language designed to address the needs of large-scale application development. Carried forward by members of the Mozilla project and other industry stakeholders in the late 2000s, ES4 aimed to introduce substantial language enhancements while preserving JavaScript’s dynamic nature. The proposal envisioned features such as optional static typing, a class-based object model, namespaces and modules, and a formal type system with interfaces and generics, along with improved tooling and maintainability for large codebases.

The ES4 effort sought to balance powerful new capabilities with backward compatibility and performance. Proponents argued that optional typing and more formal constructs would enable static analysis, safer refactoring, and better tooling without forcing all code to be typed. Critics emphasized complexity, maintainability, and the risk of fragmenting the JavaScript ecosystem. As debates continued, the process within ECMA International’s TC39 committee grew contentious, and a decision was reached to abandon the ES4 approach in favor of a more incremental path.

Result and legacy: ES5, published in 2009, introduced important but more conservative enhancements such as strict mode, JSON support, getters and setters, and improved object property semantics. Although ES4 itself was not standardized, several ideas from the proposal influenced later evolution. In particular, the later ES6/ES2015 standards reintroduced class syntax and modular programming concepts in a more incremental form. The broader idea of adding typings and tooling lived on outside the standard, notably in languages and tools like TypeScript and Flow.