Develop Reference

How can I delete blob files in JavaScript?

I am creating an image viewer using XMLHttpRequest. It includes this function:
public view_image(_tImagen: iConfigImagen){
var img_view = this.prop_div_vizualizador;
var _window: any = window;
var xhr = new XMLHttpRequest();
xhr.open("GET", _tImagen.url, true);
xhr.responseType = "blob";
xhr.onload = function () {
var urlCreator = _window.URL = _window.URL || _window.webkitURL;
var imageUrl = urlCreator.createObjectURL(this.response);
_tImagen.urlBlob = imageUrl;
img_view.style("background-image", "url(" + _tImagen.urlBlob + ")");
}
}
It works fine, but I am trying to delete the blob files that it generates somehow. I tried URL.revokeObjectURL(url), but that only deletes the url and not the file. How can I delete the files? Is there any way to remove them?
Thanks in advance.

The XMLHttpRequest allows you to make an HTTP request and receive a response, but it does not give you access to the file system. You cannot delete files without access to them.

xhr.onload too slow in android

I need to display image/jpeg in my web application as well as android app with same code and used the below working javascript code for the same:
var xhr = new XMLHttpRequest();
xhr.open('GET', value, true);
xhr.responseType = 'arraybuffer';
xhr.onload = function (e) {
var arrayBufferView = new Uint8Array( this.response );
var blob = new Blob( [ arrayBufferView ], { type: "image/jpeg" } );
var urlCreator = window.URL || window.webkitURL;
localSrc = urlCreator.createObjectURL( blob );
var img = new Image();
img.src=localSrc;
$('#jpg'+i).append(img);
};
xhr.send();
The performance is too slow when tested in android 4.4.2, like its waiting to send the xhr request after collecting all the image url's. Delay is more in android compared to web application .
How can I improve the performance ? Is there any other method to do the same with better performance?

image from localStorage url return [object ArrayBuffer]

i try using local storage for speed up my site to load image and audio file,
so i set my Pic File with java Script like this:
var req = new XMLHttpRequest();
req.onload = function (e) {
var arraybuffer = oReq.response;
}
req.open("GET", '/zTest.jpg');
req.responseType = "arraybuffer";
req.send();
req.addEventListener('readystatechange', function () {
if (req.readyState === 4) {
localStorage.setItem('photo', req.response);
}
});
in other page i use this code to return my file
var img = new Image();
img.src = localStorage.photo;
$('.imagearea').html(img);
but it don`t show Pic and my img src like this:
<img src="[object ArrayBuffer]">
note: i know local storage file size most lesser 5 Mb

The image data being saved is an ArrayBuffer hence we would first need to create a physical image before we can append it in the img tag.
let arrayBufferView = new Uint8Array( localStorage.photo );
let blob = new Blob( [ arrayBufferView ], { type: "image/jpeg" } );
let urlCreator = window.URL || window.webkitURL;
let imageUrl = urlCreator.createObjectURL( blob );
let img = new Image();
img.src = imageUrl;
$('.imagearea').html(img);

how to instantiate new file object javascript

I'm having troubles instantiating a new file object in javascript.
Here's the general gist of what I'm trying to do. There is client side code that expecting a "file" type object. I need to access the file that's located on the server (game.smc), download it to the local machine and feed it to the client side code.
I did some research and found that creating a new blob object is the first step. But in the code below the blob object remains null and is never getting populated. Does the path in the xhr.open need to have the entire url? Maybe i'm missing an entire concept here not sure.
var blob = null;
var xhr = new XMLHttpRequest();
xhr.open("GET", "/Roms/game.smc");
xhr.responseType = "blob";
xhr.onload = function()
{
blob = xhr.response;
}
xhr.send();
Once I can get the blob object populated I can then do this to convert it to a file object.
function blobToFile(theBlob, fileName) {
theBlob.lastModifiedDate = new Date();
theBlob.name = fileName;
return theBlob;
}

This is what I ended up doing. Shows how to get the blob object as well as convert it to a file type.
function autoLoadGame(fileName) {
var gameLocation = '/Content/Roms/Snes/' + fileName;
var blob = null;
var xhr = new XMLHttpRequest();
xhr.open("GET", gameLocation, true);
xhr.onreadystatechange = function () {
if (xhr.readyState == XMLHttpRequest.DONE) {
var blob = xhr.response;
var file = new File([blob], fileName, { type: '', lastModified: Date.now() });
snes_readfile(file);
}
}
xhr.responseType = "blob";
xhr.send();
}

InboxSDK - Unable to attachFiles through composeView object

I am trying to attach an attachment through the composeView object using Inboxsdk. I obtain a blob object from a remote url using the following code.
// FUNCTION TO OPEN A NEW COMPOSE BOX ONCE THE ATTACHMENT BLOB IS OBTAINED FROM REMOTE URL.
function openComposeBox(sdk, blob){
handler = sdk.Compose.registerComposeViewHandler(function(composeView){
if(blob != null){
composeView.attachFiles([blob]);
composeView.setSubject("Testing");
}
});
}
// FETCHING ATTACHMENT FILE FROM REMOTE URL
var file_btn_url = "https://api.hummingbill.com/system/invoices/invoice_files/000/033/393/original/abracadabra.txt";
var file_name = file_btn_url.split("/");
file_name = file_name[file_name.length-1];
file_type = /[^.]+$/.exec(file_name);
var blob = null;
var xhr = new XMLHttpRequest();
xhr.open("GET", file_btn_url);
xhr.responseType = "blob";
xhr.onload = function()
{
blob = xhr.response;
// blob.lastModifiedDate = new Date(); // Since it's not necessary to have it assigned, hence commented.
blob.name = file_name;
console.log(blob);
openComposeBox(sdk, blob);
}
xhr.send();
It shows an Attachment Failed error.
Although I have the correct format of blob object as required as per the documentation.
As per the documentation, I have set the filename for the blob, and passed it in an array to attachFiles function. Can you please look into it and let me know what am I missing?

Posting the solution. The code remains same as in the question, with a slight variation, wherein we convert the blob to a file, in order to make it work.
//... Same as the code in the question
// Fetching attachment file from remote url
var file_btn_url = "https://api.hummingbill.com/system/invoices/invoice_files/000/033/393/original/abracadabra.txt";
var file_name = file_btn_url.split("/");
file_name = file_name[file_name.length-1];
file_type = /[^.]+$/.exec(file_name);
var blob = null;
var xhr = new XMLHttpRequest();
xhr.open("GET", file_btn_url);
xhr.responseType = "blob";
xhr.onload = function()
{
// Solution: Convert the obtained blob to a file
// Pass the file to openComposeBox
blob = new Blob([xhr.response], { type: xhr.responseType });
var file = new File([blob], file_name);
blob.name = file_name;
openComposeBox(sdk, file);
}
xhr.send();
Hope this helps. Cheers!