Ash Blue Ash Blue - 3 months ago 31
Javascript Question

JavaScript blob filename without link

How do you set the name of a blob file in JavaScript when force downloading it through window.location?

function newFile(data) {
var json = JSON.stringify(data);
var blob = new Blob([json], {type: "octet/stream"});
var url = window.URL.createObjectURL(blob);
window.location.assign(url);
}


Running the above code downloads a file instantly without a page refresh that looks like bfefe410-8d9c-4883-86c5-d76c50a24a1d. I want to set the filename as my-download.json instead.

kol kol
Answer

The only way I'm aware of is the trick used by FileSaver.js:

  1. Create a hidden <a> tag.
  2. Set its href attribute to the blob's URL.
  3. Set its download attribute to the filename.
  4. Click on the <a> tag.

Here is a simplified example (jsfiddle):

var saveData = (function () {
    var a = document.createElement("a");
    document.body.appendChild(a);
    a.style = "display: none";
    return function (data, fileName) {
        var json = JSON.stringify(data),
            blob = new Blob([json], {type: "octet/stream"}),
            url = window.URL.createObjectURL(blob);
        a.href = url;
        a.download = fileName;
        a.click();
        window.URL.revokeObjectURL(url);
    };
}());

var data = { x: 42, s: "hello, world", d: new Date() },
    fileName = "my-download.json";

saveData(data, fileName);

I wrote this example just to illustrate the idea, in production code use FileSaver.js instead.

Notes

  • Older browsers don't support the "download" attribute, since it's part of HTML5.
  • Some file formats are considered insecure by the browser and the download fails. Saving JSON files with txt extension works for me.