Prompt file download with XMLHttpRequest

Question

I'm aware that jQuery's ajax method cannot handle downloads, and I do not want to add a jQuery plugin to do this.

I want to know how to send POST data with XMLHttpRequest to download a file.

Here's what I've tried:

var postData = new FormData(); postData.append('cells', JSON.stringify(output));  var xhr = new XMLHttpRequest(); xhr.open('POST', '/export/', true); xhr.setRequestHeader("X-CSRFToken", csrftoken); xhr.responseType = 'arraybuffer'; xhr.onload = function (e) {     console.log(e);     console.log(xhr); } xhr.send(postData); 

I'm working with Django, and the file appears to be sending back to the client successfully. In the network tab in Chrome, I can see gibberish in the preview tab (which I expect). But I want to send back a zip file, not a text representation of the zip file. Here's the Django back end:

wrapper = FileWrapper(tmp_file) response = HttpResponse(wrapper, content_type='application/zip') response['Content-Disposition'] = "attachment; filename=export.zip" response['Content-Length'] = tmp_file.tell() return response 

I've searched this for hours now without finding a proper example on how to do this with XMLHttpRequests. I don't want to create a proper html form with a POST action because the form data is rather large, and dynamically created.

Is there something wrong with the above code? Something I'm missing? I just don't know how to actually send the data to the client as a download.

Answer 1

If you set the XMLHttpRequest.responseType property to 'blob' before sending the request, then when you get the response back, it will be represented as a blob. You can then save the blob to a temporary file and navigate to it.

var postData = new FormData(); postData.append('cells', JSON.stringify(output));  var xhr = new XMLHttpRequest(); xhr.open('POST', '/export/', true); xhr.setRequestHeader('X-CSRFToken', csrftoken); xhr.responseType = 'blob'; xhr.onload = function (e) {     var blob = e.currentTarget.response;     var contentDispo = e.currentTarget.getResponseHeader('Content-Disposition');     // https://stackoverflow.com/a/23054920/     var fileName = contentDispo.match(/filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/)[1];     saveOrOpenBlob(blob, fileName); } xhr.send(postData); 

And here's an example implementation of saveOrOpenBlob:

function saveOrOpenBlob(blob, fileName) {     window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;     window.requestFileSystem(window.TEMPORARY, 1024 * 1024, function (fs) {         fs.root.getFile(fileName, { create: true }, function (fileEntry) {             fileEntry.createWriter(function (fileWriter) {                 fileWriter.addEventListener("writeend", function () {                     window.location = fileEntry.toURL();                 }, false);                 fileWriter.write(blob, "_blank");             }, function () { });         }, function () { });     }, function () { }); } 

If you don't care about having the browser navigate to the file when it's a viewable file type, then making a method that always saves directly to file is much simpler:

function saveBlob(blob, fileName) {     var a = document.createElement('a');     a.href = window.URL.createObjectURL(blob);     a.download = fileName;     a.dispatchEvent(new MouseEvent('click')); } 

Answer 2

UPDATE: this answer is not accurate anymore since the introduction of Blob API. Please refer to Steven's answer for details.

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ORIGINAL ANSWER:

XHR request will not trigger file download. I can't find explicit requirement, but W3C doc on XMLHttpRequest doesn't describe any special reaction on content-disposition=attachment responses either

You could download file by window.open() in separate tab, if it was not POST request. Here it was suggested to use a hidden form with target=_blank