Use Blob on firefox add-on

Question

Been trying to get the following code to work in firefox add-on:

var oMyForm = new FormData();

oMyForm.append("username", "Groucho");
oMyForm.append("accountnum", 123456); // number 123456 is immediately converted to string "123456"

// HTML file input user's choice...
oMyForm.append("userfile", fileInputElement.files[0]);

// JavaScript file-like object...
var oFileBody = '<a id="a"><b id="b">hey!</b></a>'; // the body of the new file...
var oBlob = new Blob([oFileBody], { type: "text/xml"});

oMyForm.append("webmasterfile", oBlob);

var oReq = new XMLHttpRequest();
oReq.open("POST", "http://foo.com/submitform.php");
oReq.send(oMyForm);

from https://developer.mozilla.org/en-US/docs/Web/Guide/Using_FormData_Objects?redirectlocale=en-US&redirectslug=Web%2FAPI%2FFormData%2FUsing_FormData_Objects

So I know I have to use XPCOM, but I can't find the equivalent. I found this so far:

var oMyForm = Cc["@mozilla.org/files/formdata;1"].createInstance(Ci.nsIDOMFormData);

oMyForm.append("username", "Groucho");
oMyForm.append("accountnum", 123456); // number 123456 is immediately converted to string "123456"

// JavaScript file-like object...
var oFileBody = '<a id="a"><b id="b">hey!</b></a>'; // the body of the new file...
var oBlob = Cc["@mozilla.org/files/file;1"].createInstance(Ci.nsIDOMFile, [oFileBody], { type: "text/xml"});

oMyForm.append("webmasterfile", oBlob);

var oReq = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(Ci.nsIXMLHttpRequest);
oReq.open("POST", "http://localhost:3000");
oReq.send(oMyForm);

Essentially the problem is var oBlob = Cc["@mozilla.org/files/file;1"].createInstance(Ci.nsIDOMFile, [oFileBody], { type: "text/xml"}); because "@mozilla.org/files/file;1" or Ci.nsIDOMFile is incorrect. Note that nsIDOMFile is inherits from nsIDOMBlob.

Anyone know what to do?

Thanks a bunch.

Answer 1

Let's cheat a little to answer this:

• JS Code Modules actually have Blob and File, while SDK modules do not :(
• Cu.import() will return the full global of a code module, incl. Blob.
• Knowing that, we can just get a valid Blob by importing a known module, such as Services.jsm

Complete, tested example, based on your code:

const {Cc, Ci, Cu} = require("chrome");
// This is the cheat ;)
const {Blob, File} = Cu.import("resource://gre/modules/Services.jsm", {});

var oMyForm = Cc["@mozilla.org/files/formdata;1"].createInstance(Ci.nsIDOMFormData);

oMyForm.append("username", "Groucho");
oMyForm.append("accountnum", 123456); // number 123456 is immediately converted to string "123456"

// JavaScript file-like object...
var oFileBody = '<a id="a"><b id="b">hey!</b></a>'; // the body of the new file...
var oBlob = Blob([oFileBody], { type: "text/xml"});

oMyForm.append("webmasterfile", oBlob, "myfile.html");

var oReq = Cc["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(Ci.nsIXMLHttpRequest);
oReq.open("POST", "http://example.org/");
oReq.send(oMyForm);