I want to convert from ArrayBuffer (lets say 100MB) to Blob then back from Blob to ArrayBuffer without duplicating the data.
FileReader / XMLHttpRequest do duplicate the data, so is there an other way?
var b = new Blob([new Uint8Array(someArrayBuffer)]);
PS: I want to make cross-tab communication of large read only buffer without duplicating it, e.g. a local ArrayBuffer is 500MB I want to use it in multiple tabs without duplicating the data.
There might be ways to convert a Blob to an ArrayBuffer without a FileReader or XHR, but they would all duplicate the data anyway.
But it sounds that what you need is not to convert from a Blob to an ArrayBuffer, but rather to share your ArrayBuffer or Blob across tabs.
For this, you've got multiple ways:
Store the ArrayBuffer/Blob on the main page, and access it from the children pages directly, like you could access any other global variables:
// in parent
window.myArrayBuffer = buffer;
// in child
var buf = window.opener.myArrayBuffer;
doSomethingWithBuffer(buf);
If you need to access the ArrayBuffer only in one tab at a time, then you can transfer its buffer to the other pages, with the postMessage API.
// in parent
child.postMessage(myArrayBuffer, 'origin', [myArrayBuffer]);
// here myArrayBuffer's buffer is *transferred* to child,
// it can't be accessed by parent anymore
// in child
window.onmessage = e => {
buf = e.data;
...
If you only need to display a Blob on different but from same-origin windows, then use a blobURI. It will only create a pointer to the data in memory, and lock this data from Garbage Collection until your docs die, but will not duplicate the data.
If you don't need to support IE nor Safari, you may even consider SharedWorkers on which you will first transfer your ArrayBuffer, and let all your tabs ask it to perform calculations, based on the same data.
varor anything else..FileReader()is robust, why you don't want to use it ?