How to instantiate a File object in JavaScript?

Now you can!

var parts = [
  new Blob(['you construct a file...'], {type: 'text/plain'}),
  ' Same way as you do with blob',
  new Uint16Array([33])
];

// Construct a file
var file = new File(parts, 'sample.txt', {
    lastModified: new Date(0), // optional - default = now
    type: "overide/mimetype" // optional - default = ''
});

var fr = new FileReader();

fr.onload = function(evt){
   document.body.innerHTML = evt.target.result + "<br><a href="+URL.createObjectURL(file)+" download=" + file.name + ">Download " + file.name + "</a><br>type: "+file.type+"<br>last modified: "+ file.lastModifiedDate
}

fr.readAsText(file);

According to the W3C File API specification, the File constructor requires 2 (or 3) parameters.

So to create a empty file do:

var f = new File([""], "filename");
  • The first argument is the data provided as an array of lines of text;
  • The second argument is the filename ;

  • The third argument looks like:

    var f = new File([""], "filename.txt", {type: "text/plain", lastModified: date})

It works in FireFox, Chrome and Opera, but not in Safari or IE/Edge.

Tags:

Javascript

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