Access file content from browser #javascript #js #nodejs

Oscar Brito

On my latest contribution to I needed to access the file's bytes to calculate an HASH value from the browser.

To access the file's content you need to get a dataTranfer object like:

$('#search_field').bind('drop', function(e, ev) {
var files = e.originalEvent.dataTransfer.files;
$.each(files, function(index, file) {


Then you can read the file's content with:

var reader = new FileReader();

// async callback to get file content
reader.onload = function(e){

// create a DataView for easy iteration
var view = new DataView(e.currentTarget.result);

// get little-endian number (32bits)
var n = view.getUint32(i, true);


// get the first 4 bytes
var blob = file.slice(0, 4);
// read the content from the file

The DataTranfer object is used to hold the date of the object being dragged. You can search further on:

More on this on the coming weeks...

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