Mock a File Upload Server Response

mockUpload.js

const mockUpload = (files = []) =>
  // return a promise so we can use async features like then/async/await
  new Promise((resolve, reject) => {
    // throw error if no files
    if (!files || !files.length) {
      return setTimeout(
        () => reject(new Error('Not found')),
        1250
      );
    }
    
    // create a mock server response
    const responseInit = { "status" : 200 , "statusText" : "OK" };
    const fakeBlob = [JSON.stringify({response:"Test"}, null, 2)];
    setTimeout(() => resolve(
      new Response(new Blob(fakeBlob, {type : 'application/json'}), responseInit)
    ), 1250);
  });

// do a fake upload
const uploadedFiles = [{thing: ""}];
mockUpload(uploadedFiles)
  .then((res) => {
    if (res.status !== 200) {
      throw new Error('Service error!')
    }
    return res.blob();
  })
  .then((blob) => blob.text())
  .then((result) => {
    // upload happened successfully!
    console.log('success', result);
  }).catch((error) => {
    // something went wrong with the api!
    console.log(error.toString())
  });