Using shared OpenGL context in the wroker thread...

Hello,

I have an issue using WebGL API in the worker thread (which is used to compile shaders only)...

My steps are:
1. I create 2 OpenGL contexts using SDL2...
_glContext = SDL_GL_CreateContext(_window);
SDL_GL_SetAttribute(SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1);
SDL_GLContext newCont = SDL_GL_CreateContext(_window);
_glSharedContext = newCont;

2. Make main context current to main thread:
SDL_GL_MakeCurrent(_window, _glContext);

3. Spawn worker job thread and make shared context current to the worker thread
// Inside the worker thread...
SDL_GL_MakeCurrent(_window, _glSharedContext);

4. Execute queue of shader jobs in worker thread...

All this perfectly worrking in windows build.
But in emscripten, unfortunately when i try to access any WebGL API in the worker it doesn't work:
Worker thread throws error, createShader is not a fucntion or so...
Looks like worker doesn't have any context? but SDL_GL_MakeCurrent returns 0, which means succeded.

So how to use WebGL in the workers?