Set the background color for PDF with JavaScript via C++

The following code snippets shows how to set the background color of PDF pages using the AsposePdfSetBackgroundColor function with JavaScript.

In the next example, we select the PDF file to handle.

1. Create a ‘FileReader’.
2. The AsposePdfSetBackgroundColor function is executed (hexadecimal format “#RRGGBB”, where RR-red, GG-green and BB-blue hexadecimal integers).
3. Set the background color for the PDF file and save the “ResultPdfSetBackgroundColor.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 ffilePdfSetBackgroundColor = function (e) {
      const file_reader = new FileReader();
      file_reader.onload = (event) => {
        /*Set the background color for the PDF file and save the "ResultPdfSetBackgroundColor.pdf"*/
        const json = AsposePdfSetBackgroundColor(event.target.result, e.target.files[0].name, "#426bf4", "ResultPdfSetBackgroundColor.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 ffilePdfSetBackgroundColor = e => {
      const file_reader = new FileReader();
      file_reader.onload = event => {
        const backgroundColor= "#426bf4";
        /*Set the background color for the PDF file and save the "ResultPdfSetBackgroundColor.pdf" - Ask Web Worker*/
        AsposePDFWebWorker.postMessage({ "operation": 'AsposePdfSetBackgroundColor', "params": [event.target.result, e.target.files[0].name, backgroundColor, "ResultPdfSetBackgroundColor.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;
      }