res.setHeader(“Set-Cookie”, …) is not setting the cookie in Node / Express

I have tried

  res.setHeader(
    "Set-Cookie",
    cookie.serialize("name", "name2", { path: "/", domain: "localhost" })

and

  res.setHeader(
    "Set-Cookie",
    cookie.serialize("name", "name2"))

and I have tried to set the cookie outright with

res.setHeader(
    "Set-Cookie",
    "name=name"})

but no cookie is set when I examine the res, and no cookie is received in my frontend. Everything is run locally. I do not understand why.

Answer

I found the answer. When using fetch() from the front end I didn’t set the credentials flag to include. When I included the flag it worked instantly.

  return await fetch(
    `url`,
    { credentials: "include" }