docs/pwa-features/file-access-api.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />

    <title>File Access API Demo</title>
  </head>
  <body>
    <h1>
      File Access API
    </h1>

    <p>
      More details can be found in the
      <a
        href="https://docs.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/open/?tabs=cmd-Windows"
        >browsers devtools console</a
      >
    </p>

    <button onclick="chooseFile()">
      Open File
    </button>

    <button onclick="saveFile()">
      Save File
    </button>

    <script>
      let file;
      
      async function chooseFile() {
        const fileHandles = await window.showOpenFilePicker({
          startIn: "pictures"
        });
        file = await fileHandles[0].getFile();

        if (file) {
          console.log(file);

          const img = new Image();
          img.src = URL.createObjectURL(file);

          document.body.append(img);
        }
      }

      async function saveFile() {
        const options = {
          types: [
            {
              description: "Image Files",
              accept: {
                "image/png": [".png"]
              }
            }
          ]
        };
        const handle = await window.showSaveFilePicker(options);
        
        const writable = await handle.createWritable();
        await writable.write(file);
        await writable.close();
      }
    </script>
  </body>
</html>