Is there a similarity to CUDA for WebGL?

Question

WebGL

At least very approximate, at least very truncated?
For example, a popular use case for WebGL is drawing the Mandelbrot set. You can force the GPU to calculate and draw a fractal. But to get this picture for yourself in the form of an array - is it possible or not?
Is it possible, say, to form a texture, then process it in a certain way with shaders, and then get this processed data back in JS?
So far, I have the feeling that it is impossible - what fell into the raster is gone. And googling does nothing. But I'm still very familiar with WebGL very superficially. If I missed something - tell me the link, what to read.