Generating SHA1 checksum of file in DropzoneJS - sha1

Question

In order to upload a file to Backblaze B2 directly from the browser, I need to send the X-Bz-Content-Sha1 header.
This header is the SHA1 of the added file.
This is from an example using raw JS and not DropzoneJS:
const file = uploadFileInput.files[0];
const reader = new FileReader();
reader.onload = function () {
const hash = CryptoJS.SHA1(CryptoJS.enc.Latin1.parse(reader.result));
/* snip */
xhr.setRequestHeader("X-Bz-Content-Sha1", hash);
};
reader.readAsBinaryString(file);
How can I generate a SHA1 of the file I add into DropzoneJS?
Here's my DropzoneJS code:
let myDropzone = new Dropzone("#dropzone", {
acceptedFiles: "image/jpeg,image/jpg",
maxFilesize: 100,
init: function () {
this.on("addedfile", function (file) {
fetch("/api/presign-upload-url", {
headers: {
"Content-Type": "application/json",
"Accept": "application/json",
"X-Requested-With": "XMLHttpRequest",
"X-CSRF-Token": csrfToken
},
method: "post",
credentials: "same-origin",
body: JSON.stringify({
key: file.name
})
})
.then(function (response) {
return response.json();
)
.then(function (json) {
console.log(file);
// I don't know how to generate the SHA1 here, `file`
// seems like the wrong object to work with?
let hash = "2";
myDropzone.options.headers = {
"Content-Type": file.type,
"Authorization": json.upload_url.authorizationToken,
"X-Bz-File-Name": file.name,
"X-Bz-Content-Sha1": hash,
};
myDropzone.options.url = json.upload_url.uploadUrl;
myDropzone.processFile(file);
});
});
}
});