JavaScript：有条件地处理获取响应

Question

I have a fetch() request returning a Response object that is either a zip file (blob) or a JSON if there was an error with the request. The code I have successfully processes the zip file and sends it to the users Downloads folder. When a JSON response is returned, the code creates a empty/corrupt zip file.

How would I go about conditionally processing the Response object so that it prevents a file from being downloaded if it is a JSON? I would also like to store Response.json() in a variable?

await fetch(params)
.then(res => res.blob())
.then(blob => {
   let url = window.URL.createObjectURL(blob);
   let a = document.createElement('a');
   a.href = url;
   a.download = name + ".zip";
   document.body.appendChild(a); 
   a.click();
   a.remove();  //afterwards we remove the element
}).catch(err => console.error(err));

Answer 1

Thanks for the suggestions all. Per @Barmer and @Bergi suggestions I was able to redefine the API so that my error content is now just inside of a header. The solution I found looks like this:

await fetch(params)
.then(function(response) {
   if (response.headers.get('X-Error') == 'False') {
      return response.blob()
         .then(blob => {
            let url = window.URL.createObjectURL(blob);
            let a = document.createElement('a');
            a.href = url;
            a.download = name + ".zip";
            document.body.appendChild(a);
            a.click();
            a.remove();
         }).catch(err => console.error(err))
   }
   //process error from backend
   console.log(response.headers.get('X-Error'))
})