Per-chart export: copy/download spec and PNG/SVG from the preview header

src/app/infrastructure/file-transfer.ts

@@ -7,10 +7,13 @@
  * than Blobs and anchors.
  */
 
-/** Trigger a client-side download of `json` text as `filename`. */
-export function downloadJson(filename: string, json: string): void {
-  const blob = new Blob([json], { type: 'application/json' });
-  const url = URL.createObjectURL(blob);
+/**
+ * Trigger a download of an already-built object/data `url` as `filename`. A
+ * `blob:` URL is revoked right after the click; a `data:` URL needs no cleanup.
+ * Used by the per-chart export for an image URL produced by the Vega view
+ * (`RenderHandle.toImageURL`).
+ */
+export function downloadUrl(filename: string, url: string): void {
   const a = document.createElement('a');
   a.href = url;
   a.download = filename;
@@ -18,10 +21,22 @@ export function downloadJson(filename: string, json: string): void {
   document.body.appendChild(a);
   a.click();
   a.remove();
-  URL.revokeObjectURL(url);
+  if (url.startsWith('blob:')) URL.revokeObjectURL(url);
+}
+
+/** Trigger a client-side download of `json` text as `filename`. */
+export function downloadJson(filename: string, json: string): void {
+  const url = URL.createObjectURL(new Blob([json], { type: 'application/json' }));
+  downloadUrl(filename, url);
 }
 
 /** Read a picked file's text content (rejects on an unreadable file). */
 export function readTextFile(file: File): Promise<string> {
   return file.text();
 }
+
+/** Copy `text` to the clipboard (rejects when the browser blocks access). The
+ *  one place outside a component that touches the clipboard API. */
+export function copyText(text: string): Promise<void> {
+  return navigator.clipboard.writeText(text);
+}