Docs show that glBindFramebuffer() only takes GL_FRAMEBUFFER in WebAssembly…
in WebGL 1 (WebGLRenderingContext, which provides OpenGL ES 2.0).
WebGL 2 (WebGL2RenderingContext) provides OpenGL ES 3.0 rendering context, which supports GL_DRAW_FRAMEBUFFER and GL_READ_FRAMEBUFFER as well.
UPDATE: I guess that’s WebGL, not WebAssembly. But I suspect there may be something similar going on (OpenGL ES 2.0 vs. 3.0).