Asymptotic complexity of slicing / merging drops

Question

I want to work with JavaScript blocks. But I'm not sure about the performance of some operations. So in this simple example ...

let n = 10; // not a constant :-)
let blob = e.dataTransfer.files[0]; // some file from user...

let blob1 = blob.slice(0, n); // O(1) or O(n)?
let blob2 = blob.slice(n); // O(1), O(n), O(blob2.length) or O(blob.length)?
let merged = new Blob([blob1, blob2]); // O(1) or O(blob.length)?

URL.createObjectURL(merged); // O(blob.length) - just to ensure, that blob will be used...

I am interested in both temporal and spatial complexity.

Answer 1

.
WebKit :
https://github.com/WebKit/webkit/blob/master/Source/WebCore/platform/network/BlobRegistryImpl.cpp#L182
Firefox - :
https://hg.mozilla.org/mozilla-central/file/d8e238b811d3/dom/file
.
. .

WebKit, Blob.slice - O (blob.length), startIndex endIndex.
Blob ([b1, b2..]) - O (b1.length + b2.length +...)
URL.createObjectURL Blob, O (1).

Blob , , Blob, . Blob .

Blobs, :

var container = document.getElementById('container');
var getReaderPromise = function(bl) {
  var blReader = new FileReader();
  return new Promise(function(resolve, reject) {
    blReader.onload = function() { resolve(blReader.result) };
    blReader.readAsArrayBuffer(bl);
  });
}

var showContent = function(arrbuf) {
  console.log(String.fromCharCode.apply(null, new Uint8Array(arrbuf)));
}

var foo = new Blob('abcdefghjklmnopqrstuvwxyz'.split(''), {type : 'text/plain'});
var promiseFoo = getReaderPromise(foo);
var foores = undefined;
promiseFoo.then(function(res) {
  foores = res;
});

var bar1 = foo.slice(2,10);
var promiseBar1 = getReaderPromise(bar1);
var bar1res = undefined;
promiseBar1.then(function(res) {
  bar1res = res;
});

var bar2 = foo.slice(12,20);
var promiseBar2 = getReaderPromise(bar2);
var bar2res = undefined;
promiseBar2.then(function(res) {
  bar2res = res;
});

var bars = new Blob([bar1, bar2]);
var promiseBars = getReaderPromise(bars);
var barsres = undefined;
promiseBars.then(function(res) {
  barsres = res;
});

Promise.all([promiseFoo, promiseBar1, promiseBar2, promiseBars]).then(function() {
  showContent(foores);
  showContent(bar1res);
  showContent(bar2res);
  showContent(barsres);

  var bar2arr = new Uint8Array(bar2res);
  bar2arr[4] = '2'.charCodeAt();

  showContent(bar2res);
  showContent(barsres);
  showContent(foores);


  var url = URL.createObjectURL(bars);
  console.log(url);
  container.innerHTML += '<iframe src="' + url + '"></iframe>';
  var barsarr = new Uint8Array(barsres);
  barsarr[4] = '5'.charCodeAt();
  container.innerHTML +=  '<iframe src="' + url + '"></iframe>';
  url = URL.createObjectURL(bars);
  console.log(url);
  container.innerHTML += '<iframe src="' + url + '"></iframe>';
});

(http://www.kurilo.su/stackoverflow/46085675/)
, Blob .
, O (1). , O (n), , WebKit, O (blob.length).