Rotate PDF Pages with JavaScript via C++

This section describes how to change the page orientation from landscape to portrait and vice versa in an existing PDF file using JavaScript via C++.

1. Create a ‘FileReader’.
2. The AsposePdfRotateAllPages function is executed.
3. The name of the resulting file is set, in this example “ResultRotation.pdf”.
4. Next, if the ‘json.errorCode’ is 0, then your DownloadFile is given the name you specified earlier. If the ‘json.errorCode’ parameter is not equal to 0 and, accordingly, there will be an error in your file, then information about such an error will be contained in the ‘json.errorText’ file.
5. As a result, the DownloadFile function generates a link and allows you to download the resulting file to the user’s operating system.

  var ffileRotateAllPages = function (e) {
    const file_reader = new FileReader();
    file_reader.onload = (event) => {
      /*rotate all pages PDF-file and save the "ResultRotation.pdf"*/
      const json = AsposePdfRotateAllPages(event.target.result, e.target.files[0].name, Module.Rotation.on270, "ResultRotation.pdf");
      if (json.errorCode == 0) document.getElementById('output').textContent = json.fileNameResult;
      else document.getElementById('output').textContent = json.errorText;
      /*make a link to download the result file*/
      DownloadFile(json.fileNameResult, "application/pdf");
    };
    file_reader.readAsArrayBuffer(e.target.files[0]);
  };

Using Web Workers

    /*Create Web Worker*/
    const AsposePDFWebWorker = new Worker("AsposePDFforJS.js");
    AsposePDFWebWorker.onerror = evt => console.log(`Error from Web Worker: ${evt.message}`);
    AsposePDFWebWorker.onmessage = evt => document.getElementById('output').textContent = 
      (evt.data == 'ready') ? 'loaded!' :
        (evt.data.json.errorCode == 0) ?
          `Result:\n${DownloadFile(evt.data.json.fileNameResult, "application/pdf", evt.data.params[0])}` :
          `Error: ${evt.data.json.errorText}`;

    /*Event handler*/
    const ffileRotateAllPages = e => {
      const file_reader = new FileReader();
      file_reader.onload = event => {
        const rotation = 'Module.Rotation.on270';
        /*Rotate PDF-pages and save the "ResultRotation.pdf" - Ask Web Worker*/
        AsposePDFWebWorker.postMessage(
          { "operation": 'AsposePdfRotateAllPages',
            "params": [event.target.result, e.target.files[0].name, rotation, "ResultRotation.pdf"] },
          [event.target.result]
        );
      };
      file_reader.readAsArrayBuffer(e.target.files[0]);
    };

    /*Make a link to download the result file*/
    const DownloadFile = (filename, mime, content) => {
        mime = mime || "application/octet-stream";
        var link = document.createElement("a"); 
        link.href = URL.createObjectURL(new Blob([content], {type: mime}));
        link.download = filename;
        link.innerHTML = "Click here to download the file " + filename;
        document.body.appendChild(link); 
        document.body.appendChild(document.createElement("br"));
        return filename;
      }