Client Side - Compute the SHA-256 hash of a file that is selected in a file input

Code

<html> <body> <input type="file" id="myfile" onchange="onMyfileChange(this)" /> <script type="text/javascript"> function onMyfileChange(fileInput) { if (fileInput.files[0] == undefined) { return; } var filename = fileInput.files[0].name; // var filesize = fileInput.files[0].size; var reader = new FileReader(); reader.onload = function (ev) { console.log('File', filename, ':'); // crypto.subtle .digest('SHA-256', ev.target.result) .then((hashBuffer) => { // Convert hex to hash, see https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/digest#converting_a_digest_to_a_hex_string const hashArray = Array.from(new Uint8Array(hashBuffer)); const hashHex = hashArray .map((b) => b.toString(16).padStart(2, '0')) .join(''); // convert bytes to hex string console.log(hashHex); }) .catch((ex) => console.error(ex)); }; reader.onerror = function (err) { console.error('Failed to read file', err); }; reader.readAsArrayBuffer(fileInput.files[0]); } </script> </body> </html>