javascript - Prompt file download with XMLHttpRequest

Javascript - Prompt file download with XMLHttpRequest

To prompt a file download using XMLHttpRequest in JavaScript, you need to perform several steps, including setting the response type and handling the blob data appropriately. Here's a detailed approach to achieve this:

Steps to Prompt File Download with XMLHttpRequest

  1. Create XMLHttpRequest Object: Create a new instance of XMLHttpRequest.

  2. Set Response Type: Set the response type to "blob" to handle binary data (like files) from the server.

  3. Open and Send Request: Open a GET request to the server endpoint that serves the file, and send the request.

  4. Handle Response: In the onload event handler of XMLHttpRequest, handle the downloaded file (blob data).

  5. Create Download Link: Create an <a> element dynamically in JavaScript.

  6. Set Download Attributes: Set the href attribute of the <a> element to a URL created from the blob data using URL.createObjectURL(). Also, set download attribute to specify the default filename for the downloaded file.

  7. Append Link and Trigger Download: Append the <a> element to the document body, trigger a click event on the link to prompt the download, and then remove the link from the document.

Here's an example implementation:

function downloadFile(url) { var xhr = new XMLHttpRequest(); xhr.open('GET', url, true); xhr.responseType = 'blob'; xhr.onload = function() { if (xhr.status === 200) { var blob = xhr.response; var filename = getFilenameFromResponse(xhr); // Create a link element, set the URL and attributes var a = document.createElement('a'); a.href = window.URL.createObjectURL(blob); a.download = filename || 'download'; a.style.display = 'none'; // Append the link to the body and trigger the download document.body.appendChild(a); a.click(); // Clean up document.body.removeChild(a); } }; xhr.send(); } function getFilenameFromResponse(xhr) { // Extract filename from Content-Disposition header if available var contentDisposition = xhr.getResponseHeader('Content-Disposition'); if (contentDisposition && contentDisposition.indexOf('attachment') !== -1) { var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/; var matches = filenameRegex.exec(contentDisposition); if (matches != null && matches[1]) { return matches[1].replace(/['"]/g, ''); } } return null; } // Usage example var fileUrl = 'https://example.com/download/file.pdf'; downloadFile(fileUrl);

Explanation:

  • downloadFile(url) Function:

    • Initiates a GET request to url using XMLHttpRequest.
    • Sets responseType to 'blob' to handle binary data.
    • On successful response (xhr.onload), retrieves the blob data (xhr.response).
    • Uses a dynamically created <a> element to initiate the download by setting its href to the blob URL (URL.createObjectURL(blob)).
    • Sets download attribute to specify the filename for the downloaded file.
    • Appends the <a> element to the document body, triggers a click event on it to start the download, and removes the element after the download completes.

  • getFilenameFromResponse(xhr) Function:

    • Extracts the filename from the Content-Disposition header of the HTTP response, if available. This header is commonly used to suggest a filename for downloads.

  • Usage Example:

    • fileUrl is the URL of the file you want to download. Replace it with your actual file URL.

Notes:

  • Cross-Origin Requests: Ensure that the server allows cross-origin requests if the file is hosted on a different domain.
  • Browser Compatibility: This approach is compatible with modern browsers that support XMLHttpRequest and Blob objects.
  • Filename Handling: The getFilenameFromResponse function attempts to extract the filename from the Content-Disposition header. Adjust it as needed based on your server's response headers.

By following these steps, you can effectively prompt a file download using XMLHttpRequest in JavaScript, enabling users to download files from your web application dynamically. Adjust the code as necessary for your specific use case and server-side setup.

Examples

  1. JavaScript XMLHttpRequest download file example: How to initiate a file download using XMLHttpRequest in JavaScript.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/file.pdf', true); xhr.responseType = 'blob'; xhr.onload = function() { var blob = xhr.response; var fileName = 'downloaded_file.pdf'; var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); var url = window.URL.createObjectURL(blob); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads a PDF file from http://example.com/file.pdf using XMLHttpRequest, creates a hidden anchor (<a>) element, and triggers the download upon successful completion (xhr.onload).

  2. JavaScript XMLHttpRequest download text file: Initiating a text file download with XMLHttpRequest in JavaScript.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/file.txt', true); xhr.onload = function() { var textContent = xhr.responseText; var fileName = 'downloaded_file.txt'; var blob = new Blob([textContent], { type: 'text/plain' }); var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads a text file (file.txt) using XMLHttpRequest, retrieves its content (xhr.responseText), creates a Blob object, and prompts the user to download it.

  3. JavaScript XMLHttpRequest download CSV file: Downloading a CSV file with XMLHttpRequest and prompting the download.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/data.csv', true); xhr.onload = function() { var csvContent = xhr.responseText; var fileName = 'downloaded_data.csv'; var blob = new Blob([csvContent], { type: 'text/csv' }); var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads a CSV file (data.csv) using XMLHttpRequest, creates a Blob object with its content, and initiates the download with a dynamically created anchor (<a>) element.

  4. JavaScript XMLHttpRequest download image file: Downloading an image file with XMLHttpRequest and prompting the download.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/image.jpg', true); xhr.responseType = 'blob'; xhr.onload = function() { var blob = xhr.response; var fileName = 'downloaded_image.jpg'; var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads an image file (image.jpg) from a URL using XMLHttpRequest, handles the response as a blob, and triggers the download.

  5. JavaScript XMLHttpRequest download binary file: Downloading a binary file with XMLHttpRequest and prompting the download.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/file.bin', true); xhr.responseType = 'arraybuffer'; xhr.onload = function() { var arrayBuffer = xhr.response; var fileName = 'downloaded_file.bin'; var blob = new Blob([arrayBuffer], { type: 'application/octet-stream' }); var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads a binary file (file.bin) using XMLHttpRequest with responseType set to arraybuffer, creates a Blob object, and triggers the download.

  6. JavaScript XMLHttpRequest download JSON file: Downloading a JSON file with XMLHttpRequest and prompting the download.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/data.json', true); xhr.onload = function() { var jsonData = JSON.stringify(JSON.parse(xhr.responseText), null, 2); var fileName = 'downloaded_data.json'; var blob = new Blob([jsonData], { type: 'application/json' }); var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads a JSON file (data.json) using XMLHttpRequest, converts the response to a formatted JSON string, creates a Blob object, and triggers the download.

  7. JavaScript XMLHttpRequest download with progress bar: Adding a progress bar while downloading a file with XMLHttpRequest.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/large_file.zip', true); xhr.responseType = 'blob'; xhr.onprogress = function(e) { if (e.lengthComputable) { var percentComplete = (e.loaded / e.total) * 100; console.log('Download progress: ' + percentComplete.toFixed(2) + '%'); // Update progress bar } }; xhr.onload = function() { var blob = xhr.response; var fileName = 'downloaded_file.zip'; var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Shows how to track download progress (xhr.onprogress) while downloading a large file (large_file.zip) with XMLHttpRequest.

  8. JavaScript XMLHttpRequest download file from authenticated endpoint: Downloading a file from an authenticated endpoint using XMLHttpRequest.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/secure/download', true); xhr.setRequestHeader('Authorization', 'Bearer ' + accessToken); xhr.responseType = 'blob'; xhr.onload = function() { var blob = xhr.response; var fileName = 'downloaded_file.pdf'; var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

    Description: Downloads a file (download) from an authenticated endpoint (secure/download) using XMLHttpRequest with an Authorization header (Bearer accessToken).

  9. JavaScript XMLHttpRequest download file with error handling: Implementing error handling while downloading a file with XMLHttpRequest.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/file.pdf', true); xhr.responseType = 'blob'; xhr.onload = function() { if (xhr.status === 200) { var blob = xhr.response; var fileName = 'downloaded_file.pdf'; var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); } else { console.error('Failed to download file. Status: ' + xhr.status); } }; xhr.onerror = function() { console.error('Network error occurred while downloading file.'); }; xhr.send();

    Description: Implements error handling (xhr.onerror) and status check (xhr.status === 200) while downloading a file (file.pdf) using XMLHttpRequest.

  10. JavaScript XMLHttpRequest download file with custom headers: Adding custom headers while downloading a file with XMLHttpRequest.

    var xhr = new XMLHttpRequest(); xhr.open('GET', 'http://example.com/file.pdf', true); xhr.setRequestHeader('Custom-Header', 'value'); xhr.responseType = 'blob'; xhr.onload = function() { var blob = xhr.response; var fileName = 'downloaded_file.pdf'; var url = window.URL.createObjectURL(blob); var a = document.createElement('a'); a.style.display = 'none'; document.body.appendChild(a); a.href = url; a.download = fileName; a.click(); window.URL.revokeObjectURL(url); }; xhr.send();

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