Model middleware

I have this prompt:

const refinementPrompt = await ai.prompt('textRefinement')
const result = await refinementPrompt({
  request: userRequest
});

const refinementPrompt = await ai.prompt('textRefinement')
const result = await refinementPrompt({
  request: userRequest
});

const refinementPrompt = await ai.prompt('textRefinement')
const result = await refinementPrompt({
  request: userRequest
});

const refinementPrompt = await ai.prompt('textRefinement')
const result = await refinementPrompt({
  request: userRequest
});

How do I go about adding middleware to the prompt object?