WebGL is a JavaScript interface to OpenGL ES, with some limitations. If you only want the core feature set (no extensions), it is pretty much the same API, and

WebGL is a JavaScript interface to OpenGL ES, with some limitations. If you only want the core feature set (no extensions), it is pretty much the same API, and with emscripten it is possible to write portable C, C++ or Rust code against the OpenGL ES API and have it work not only natively but also in the browser via WebGL. OpenGL ES is almost a subset of OpenGL, though there are also some ES-exclusive features. With some care it's possible to write code that works on both OpenGL ES (and WebGL if you want) and OpenGL. Annoyingly there isn't a name for the common subset that works in both APIs.