What is jscript?

JScript is Microsoft’s own implementation of the JavaScript language. It follows the ECMAScript standard but adds some Microsoft‑specific features. You’ll find it mainly in older versions of Internet Explorer and in Windows scripting environments.

Let's break it down

  • Language core: Same basic syntax as JavaScript - variables, functions, loops, objects.
  • Engine: Runs on the JScript engine built into Windows (often called “JScript.dll”).
  • Extensions: Provides extra objects for interacting with Windows components (e.g., ActiveX, COM).
  • Execution contexts: Can run inside a web page (IE), inside Windows Script Host (WSH), or on the server with classic ASP.

Why does it matter?

Understanding JScript helps you maintain legacy web applications and Windows scripts that still rely on it. It also shows how JavaScript evolved across different platforms, giving insight into compatibility and security considerations when working with older codebases.

Where is it used?

  • Classic ASP pages on older Microsoft servers.
  • Windows Script Host scripts (*.js) for automating tasks on Windows machines.
  • Internet Explorer (especially versions before Edge) for client‑side interactivity.
  • Some corporate intranet tools that were built before modern browsers became dominant.

Good things about it

  • Tight integration with Windows, allowing easy access to COM objects and system resources.
  • Simple to learn for anyone who already knows JavaScript.
  • Works out‑of‑the‑box on most Windows installations without extra runtimes.
  • Useful for quick automation scripts on Windows desktops and servers.

Not-so-good things

  • Only works reliably in Internet Explorer; modern browsers ignore JScript.
  • Lacks many newer ECMAScript features (let/const, arrow functions, modules, etc.).
  • Security risks: older JScript code can be vulnerable to script injection and ActiveX exploits.
  • Microsoft has shifted focus to Edge and standard JavaScript, so JScript receives little to no future updates.