ReferenceError: TextEncoder is not defined

I'm writing a simple addon in Firefox - 24, on Linux. I get the error:

ReferenceError: TextEncoder is not defined

when I do: var encoder = new TextEncoder(); the function I'm using is:

function write_text(filename, text) {
    var encoder = new TextEncoder();
    var data = encoder.encode(text);
    Task.spawn(function() {
       let pfh =  OS.File.open("/tmp/foo", {append: true});
       yield pfh.write(text);
       yield pfh.flush();
       yield pfh.close(); 
    });
}

Ah, you're using the SDK, I gather when re-reading the actual error of your other question.

• You need to import TextEncoder explicitly from some other module, as SDK modules lack the class.
• You need to yield OS.File.open.
• append: is only supported in Firefox 27+
• .flush() is only supported in Firefox 27+ (and a bad idea anyway). Use .writeAtomic if you need that.
• You write: true to write to a file.

Here is a full, working example I tested in Firefox 25 (main.js)

const {Cu} = require("chrome");
// It is important to load TextEncoder like this using Cu.import()
// You cannot load it by just |Cu.import("resource://gre/modules/osfile.jsm");|
const {TextEncoder, OS} = Cu.import("resource://gre/modules/osfile.jsm", {});
const {Task} = Cu.import("resource://gre/modules/Task.jsm", {});

function write_text(filename, text) {
    var encoder = new TextEncoder();
    var data = encoder.encode(text);
    filename = OS.Path.join(OS.Constants.Path.tmpDir, filename);
    Task.spawn(function() {
       let file = yield OS.File.open(filename, {write: true});
       yield file.write(data);
       yield file.close(); 
       console.log("written to", filename);
    }).then(null, function(e) console.error(e));
}

write_text("foo", "some text");