Tag Archives: Shared Access Signature

Download file from Azure storage using Javascript

.Net is an excellent framework – if you want proof of that, try to do, even very simple things, in Javascript. It feels a bit like getting out of a Tesla and travelling back in time to drive a Robin Reliant (I’ve never actually driven either of these cars, so I don’t really know if it feels like that or not!)

If you were to, for example, want to download a file from a Blob Storage container, in .Net you’re looking at about 4 lines of strongly typed code. There’s basically nothing to do, and it consistently works. If you want to do that in Javascript, there’s a Microsoft Javascript Library.

In said library, there is a function that should get a download URL for you; it’s named getUrl:

const downloadLink = blobService.getUrl(containerName, fileId, sasKey);            

If you use this (at least, when I used this), it gave me the following error:

Signature did not match

To get around this, you can build the download link manually like this:

const downloadLink = blobUri + '/' + containerName + '/' + fileId + sasKey;

Comparing the two, the former appears to escape the question mark in the SAS.

To actually download the file, you can use this:

        // https://stackoverflow.com/questions/3749231/download-file-using-javascript-jquery
        function downloadURI(uri, name) 
        {
            var link = document.createElement("a");
            link.download = name;
            link.href = uri;
            link.click();
        }

And the final download function looks like this:

        function downloadFile(sas, storageUri,
            containerName, fileId, destinationFileName) {

            var blobService = AzureStorage.Blob.createBlobServiceWithSas(storageUri, sas);
            
            const downloadLink = storageUri +'/' + containerName + '/' + fileId + sas;

            downloadURI(downloadLink, destinationFileName);
        }