refactor postRequest method, display image in iframe

sandbox.html

@@ -149,10 +149,12 @@
       getData: async data => {
         const result = await cadenzaClient.getData(data.dataType);
         if (data.dataType === 'png') {
-          const canvas = document.getElementById('canvas');
-          const ctx = canvas.getContext('2d');      
-          const imageBitmap = await createImageBitmap(result)
-          ctx.drawImage(imageBitmap, 0, 0, 300, 150);
+          const url = URL.createObjectURL(result);
+          try {
+            iframe.src = url;
+          } finally {
+            URL.revokeObjectURL(url);
+          }
         }      
       }
     };

src/cadenza.js

@@ -524,27 +524,6 @@ export class CadenzaClient {
     return promise;
   }
 
-   /**
-   * @template [T=void]
-   * @param {string} type
-   * @param {unknown} [detail]
-   * @returns {Promise<T>}
-   */
-   #postRequest(type, detail) {
-    /** @type {(() => void)[]} */
-    let unsubscribes;
-    const promise = new Promise((resolve, reject) => {
-      unsubscribes = [
-        this.#on(`${type}:success`, (event) => resolve(event.detail)),
-        this.#on(`${type}:error`, () => reject()),
-      ];
-    });
-    promise.finally(() => unsubscribes.forEach((unsubscribe) => unsubscribe()));
-    this.#postEvent(type, detail);
-    return promise;
-  }
-
-
   /**
    * Subscribe to a `postMessage()` event.
    *
@@ -617,14 +596,14 @@ export class CadenzaClient {
    */
   #postRequest(/** @type string */ type, /** @type unknown */ detail) {
     const { port1, port2 } = new MessageChannel();
-    /** @type {Promise<void>} */
+    /** @type {Promise<never>} */
     const promise = new Promise((resolve, reject) => {
       port1.onmessage = (
         /** @type MessageEvent<CadenzaEvent<never, never>> */ event,
       ) => {
         const cadenzaEvent = event.data;
         if (cadenzaEvent.type === `${type}:success`) {
-          resolve();
+          resolve(cadenzaEvent.detail);
         } else if (cadenzaEvent.type === `${type}:error`) {
           reject();
         }
@@ -691,7 +670,7 @@ export class CadenzaClient {
     return res;
   }
 
-   /**
+  /**
    * Get data from the currently shown workbook view.
    *
    * Currently, only map views are supported.

src/docs.md

@@ -308,7 +308,7 @@ button.textContent = 'Download Excel';
 button.onclick = () => cadenzaClient.downloadData('{embeddingTargetId}', 'excel');
 ```
 
-### Request Data From a Workbook View via PostMessage
+### Request Data From a Workbook View
 
 <small>API: [CadenzaClient#getData](./classes/CadenzaClient.html#getData)</small>