Download File from Bytes in JavaScript

Question

I want to download the file which is coming in the form of bytes from the AJAX response.

I tried to do it this way with the help of Blob:

var blob=new Blob([resultByte], {type: "application/pdf"});
var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download="myFileName.pdf";
link.click();

It is in fact downloading the pdf file but the file itself is corrupted.

How can I accomplish this?

Answer 1

I asked the question long time ago, so I might be wrong in some details.

It turns out that Blob needs array buffers. That's why base64 bytes need to be converted to array buffers first.

Here is the function to do that:

function base64ToArrayBuffer(base64) {
    var binaryString = window.atob(base64);
    var binaryLen = binaryString.length;
    var bytes = new Uint8Array(binaryLen);
    for (var i = 0; i < binaryLen; i++) {
       var ascii = binaryString.charCodeAt(i);
       bytes[i] = ascii;
    }
    return bytes;
 }

Here is my function to save a pdf file:

function saveByteArray(reportName, byte) {
    var blob = new Blob([byte], {type: "application/pdf"});
    var link = document.createElement('a');
    link.href = window.URL.createObjectURL(blob);
    var fileName = reportName;
    link.download = fileName;
    link.click();
};

Here is how to use these two functions together:

var sampleArr = base64ToArrayBuffer(data);
saveByteArray("Sample Report", sampleArr);

Answer 2

You just need to add one extra line and it should work. Your response is byte array from your server application

var bytes = new Uint8Array(resultByte); // pass your byte response to this constructor

var blob=new Blob([bytes], {type: "application/pdf"});// change resultByte to bytes

var link=document.createElement('a');
link.href=window.URL.createObjectURL(blob);
link.download="myFileName.pdf";
link.click();

Answer 3

Set Blob type at Blob constructor instead of at createObjectURL

var blob = new Blob([resultByte], {type: "application/pdf"});
var link = document.createElement("a");
link.href = window.URL.createObjectURL(blob);
link.download = "myFileName.pdf";
link.click();

Answer 4

As mentioned here, if you're using Axios.get() on the front-end, make sure to add the { responseType: 'blob' } option:

const res = await axios.get("/api/pdf-route", 
    { responseType: 'blob' } // <----- ***
);

And then the download is as many mentioned:

const pdfBlob = new Blob([res.data], { type: 'application/pdf' });
const downloadUrl = URL.createObjectURL(pdfBlob);
const link = document.createElement("a");
link.href = downloadUrl;
link.download = filename;
link.click();
URL.revokeObjectURL(downloadUrl);

For more info: https://stackoverflow.com/a/76126845/12056841

Answer 5

Easiest way would be converting bytes to the base64 format and construct link as below

let link=document.createElement('a');
const mimeType = "application/pdf";
link.href=`data:${mimeType};base64,${base64Str}`;
link.download="myFileName.pdf";
link.click();

Link can be generated on backend side and retrieved from the response.
File bytes can be read as base64 string in Python as following:

with open("my-file.pdf", "rb") as file:
    base46_str = base64.b64encode(file.read()).decode("utf-8")