The WebGL specification communicates all errors via the getError / glGetError mechanism. In some cases, restrictions in WebGL semantics above and beyond those in the OpenGL ES 2.0 API require synthesizing OpenGL errors.
In such cases it would be useful to developers to be able to request additional information beyond the simple return code from getError(). Adding the following simple entry point would provide a reasonable amount of additional debugging information:
which would return a detail message, if any, for the last error code returned from a call to getError(). This information could then be included in logs or stack traces.
This is not an OpenGL bug.