How to checksum the file to be uploaded with javascript?

Question

I want to checksum the files at browser side before uploading, then checksum and compare at server side to make sure the consistent. But how can I get the pure binary data of the file and checksum it? I tried the way below, but doesn't work:

let fileSelect = document.getElementById('file')
let files = fileSelect.files
let file = files[0]

var r = new FileReader();
r.onload = function(){ console.log(r.result); };
r.readAsArrayBuffer(file);
var file_sha1 = sha1(r.result)

Check this question here http://stackoverflow.com/questions/16505333/get-the-data-of-uploaded-file-in-javascript — Luo, Mar 23 '16 at 13:33
@jayms, I use this npm library: https://www.npmjs.com/package/sha1 — Suge, Mar 24 '16 at 03:29

score 7 · Accepted Answer · answered Mar 31 '16 at 07:30

The library you are using seems to support string input only. Find a library support binary input. Eg. js-sha1. And you should hash it in the callback.

var reader = new FileReader();
reader.onload = function (event) {
  var file_sha1 = sha1(event.target.result)
};
reader.readAsArrayBuffer(file);

How to checksum the file to be uploaded with javascript?

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