fetch gives an empty response body

I just ran into this. As mentioned in this answer, using mode: "no-cors" will give you an opaque response, which doesn't seem to return data in the body.

opaque: Response for “no-cors” request to cross-origin resource. Severely restricted.

In my case I was using Express. After I installed cors for Express and configured it and removed mode: "no-cors", I was returned a promise. The response data will be in the promise, e.g.

fetch('http://example.com/api/node', {
  // mode: 'no-cors',
  method: 'GET',
  headers: {
    Accept: 'application/json',
  },
},
).then(response => {
  if (response.ok) {
    response.json().then(json => {
      console.log(json);
    });
  }
});

You will need to convert your response to json before you can access response.body

From the docs

fetch(url)
  .then(response => response.json())
  .then(json => {
    console.log('parsed json', json) // access json.body here
  })

This requires changes to the frontend JS and the headers sent from the backend.

Frontend

Remove "mode":"no-cors" in the fetch options.

fetch(
  "http://example.com/api/docs", 
  {
    // mode: "no-cors",
    method: "GET"
  }
)
  .then(response => response.text())
  .then(data => console.log(data))

Backend

When your server responds to the request, include the CORS headers specifying the origin from where the request is coming. If you don't care about the origin, specify the * wildcard.

The raw response should include a header like this.

Access-Control-Allow-Origin: *