Replace all file-downloading function with one which expects the type

src/shared/download-file.ts

-function downloadFile(
+export function downloadFile(
   content: string,
   type: string,
   filename: string,
-  document: Document,
+  /* istanbul ignore next - test seam */
+  document_ = document,
 ): void {
   const blob = new Blob([content], { type });
   const url = URL.createObjectURL(blob);
 
-  const link = document.createElement('a');
+  const link = document_.createElement('a');
   link.setAttribute('href', url);
   link.setAttribute('download', filename);
   link.style.visibility = 'hidden';
 
-  document.body.appendChild(link);
+  document_.body.appendChild(link);
   link.click();
-  document.body.removeChild(link);
+  document_.body.removeChild(link);
 
   URL.revokeObjectURL(url);
 }
-
-function buildTextFileDownloader(type: string) {
-  return (
-    text: string,
-    filename: string,
-    /* istanbul ignore next - test seam */
-    _document = document,
-  ) => downloadFile(text, type, filename, _document);
-}
-
-export const downloadJSONFile = buildTextFileDownloader('application/json');
-
-export const downloadTextFile = buildTextFileDownloader('text/plain');
-
-export const downloadCSVFile = buildTextFileDownloader('text/csv');
-
-export const downloadHTMLFile = buildTextFileDownloader('text/html');

src/shared/test/download-file-test.js

-import {
-  downloadCSVFile,
-  downloadHTMLFile,
-  downloadJSONFile,
-  downloadTextFile,
-} from '../download-file';
+import { downloadFile } from '../download-file';
 
 describe('download-file', () => {
   let fakeLink;
@@ -47,39 +42,14 @@ describe('download-file', () => {
     assert.equal('hidden', fakeLink.style.visibility);
   }
 
-  it('downloadJSONFile generates JSON file with provided data', () => {
-    const data = JSON.stringify({ foo: ['bar', 'baz'] }, null, 2);
-    const filename = 'my-file.json';
+  ['application/json', 'text/plain', 'text/csv', 'text/html'].forEach(type => {
+    it('downloadTextFile generates text file with provided data', () => {
+      const data = 'The content of the file';
+      const filename = 'my-file.txt';
 
-    downloadJSONFile(data, filename, fakeDocument);
+      downloadFile(data, type, filename, fakeDocument);
 
-    assertDownloadHappened(filename, data, 'application/json');
-  });
-
-  it('downloadTextFile generates text file with provided data', () => {
-    const data = 'The content of the file';
-    const filename = 'my-file.txt';
-
-    downloadTextFile(data, filename, fakeDocument);
-
-    assertDownloadHappened(filename, data, 'text/plain');
-  });
-
-  it('downloadCSVFile generates csv file with provided data', () => {
-    const data = 'foo,bar,baz';
-    const filename = 'my-file.csv';
-
-    downloadCSVFile(data, filename, fakeDocument);
-
-    assertDownloadHappened(filename, data, 'text/csv');
-  });
-
-  it('downloadHTMLFile generates HTML file with provided data', () => {
-    const data = '<p>Hello</p>';
-    const filename = 'my-file.html';
-
-    downloadHTMLFile(data, filename, fakeDocument);
-
-    assertDownloadHappened(filename, data, 'text/html');
+      assertDownloadHappened(filename, data, type);
+    });
   });
 });

src/sidebar/components/ShareDialog/ExportAnnotations.tsx

@@ -8,12 +8,7 @@ import {
 } from '@hypothesis/frontend-shared';
 import { useCallback, useId, useMemo, useState } from 'preact/hooks';
 
-import {
-  downloadCSVFile,
-  downloadHTMLFile,
-  downloadJSONFile,
-  downloadTextFile,
-} from '../../../shared/download-file';
+import { downloadFile } from '../../../shared/download-file';
 import type { APIAnnotationData } from '../../../types/api';
 import { annotationDisplayName } from '../../helpers/annotation-user';
 import type { UserAnnotations } from '../../helpers/annotations-by-user';
@@ -74,6 +69,16 @@ const exportFormats: ExportFormat[] = [
   },
 ];
 
+function formatToMimeType(format: ExportFormat['value']): string {
+  const typeForFormat: Record<ExportFormat['value'], string> = {
+    json: 'application/json',
+    txt: 'text/plain',
+    csv: 'text/csv',
+    html: 'text/html',
+  };
+  return typeForFormat[format];
+}
+
 /**
  * Render content for "export" tab panel: allow user to export annotations
  * with a specified filename.
@@ -200,25 +205,9 @@ function ExportAnnotations({
         const format = exportFormat.value;
         const filename = `${customFilename ?? defaultFilename}.${format}`;
         const exportData = buildExportContent(format);
+        const mimeType = formatToMimeType(format);
 
-        switch (format) {
-          case 'json': {
-            downloadJSONFile(exportData, filename);
-            break;
-          }
-          case 'txt': {
-            downloadTextFile(exportData, filename);
-            break;
-          }
-          case 'csv': {
-            downloadCSVFile(exportData, filename);
-            break;
-          }
-          case 'html': {
-            downloadHTMLFile(exportData, filename);
-            break;
-          }
-        }
+        downloadFile(exportData, mimeType, filename);
       } catch (e) {
         toastMessenger.error('Exporting annotations failed');
       }

src/sidebar/components/ShareDialog/test/ExportAnnotations-test.js

@@ -14,10 +14,7 @@ describe('ExportAnnotations', () => {
   let fakeStore;
   let fakeAnnotationsExporter;
   let fakeToastMessenger;
-  let fakeDownloadJSONFile;
-  let fakeDownloadTextFile;
-  let fakeDownloadCSVFile;
-  let fakeDownloadHTMLFile;
+  let fakeDownloadFile;
   let fakeSuggestedFilename;
   let fakeCopyPlainText;
   let fakeCopyHTML;
@@ -48,10 +45,7 @@ describe('ExportAnnotations', () => {
       error: sinon.stub(),
       success: sinon.stub(),
     };
-    fakeDownloadJSONFile = sinon.stub();
-    fakeDownloadTextFile = sinon.stub();
-    fakeDownloadCSVFile = sinon.stub();
-    fakeDownloadHTMLFile = sinon.stub();
+    fakeDownloadFile = sinon.stub();
     fakeStore = {
       defaultAuthority: sinon.stub().returns('example.com'),
       isFeatureEnabled: sinon.stub().returns(true),
@@ -74,10 +68,7 @@ describe('ExportAnnotations', () => {
 
     $imports.$mock({
       '../../../shared/download-file': {
-        downloadJSONFile: fakeDownloadJSONFile,
-        downloadTextFile: fakeDownloadTextFile,
-        downloadCSVFile: fakeDownloadCSVFile,
-        downloadHTMLFile: fakeDownloadHTMLFile,
+        downloadFile: fakeDownloadFile,
       },
       '../../helpers/export-annotations': {
         suggestedFilename: fakeSuggestedFilename,
@@ -408,21 +399,21 @@ describe('ExportAnnotations', () => {
     [
       {
         format: 'json',
-        getExpectedInvokedDownloader: () => fakeDownloadJSONFile,
+        expectedMimeType: 'application/json',
       },
       {
         format: 'txt',
-        getExpectedInvokedDownloader: () => fakeDownloadTextFile,
+        expectedMimeType: 'text/plain',
       },
       {
         format: 'csv',
-        getExpectedInvokedDownloader: () => fakeDownloadCSVFile,
+        expectedMimeType: 'text/csv',
       },
       {
         format: 'html',
-        getExpectedInvokedDownloader: () => fakeDownloadHTMLFile,
+        expectedMimeType: 'text/html',
       },
-    ].forEach(({ format, getExpectedInvokedDownloader }) => {
+    ].forEach(({ format, expectedMimeType }) => {
       it('downloads a file using user-entered filename appended with proper extension', async () => {
         const wrapper = createComponent();
         const filenameInput = wrapper.find(
@@ -436,11 +427,11 @@ describe('ExportAnnotations', () => {
 
         submitExportForm(wrapper);
 
-        const invokedDownloader = getExpectedInvokedDownloader();
-        assert.calledOnce(invokedDownloader);
+        assert.calledOnce(fakeDownloadFile);
         assert.calledWith(
-          invokedDownloader,
+          fakeDownloadFile,
           sinon.match.any,
+          expectedMimeType,
           `my-filename.${format}`,
         );
       });
@@ -456,7 +447,7 @@ describe('ExportAnnotations', () => {
 
         submitExportForm(wrapper);
 
-        assert.notCalled(fakeDownloadJSONFile);
+        assert.notCalled(fakeDownloadFile);
         assert.calledOnce(fakeAnnotationsExporter.buildJSONExportContent);
         assert.calledWith(
           fakeToastMessenger.error,