Writing files in Brackets extensions

main.js

define(function () {
    "use strict";
    
    var AppInit         = brackets.getModule("utils/AppInit"),
        FileSystem      = brackets.getModule("filesystem/FileSystem"),
        ProjectManager  = brackets.getModule("project/ProjectManager");

    AppInit.appReady(function () {
        var filename = ProjectManager.getProjectRoot().fullPath + "hello-world.txt";
        FileSystem.getFileForPath(filename).write("Hello world!\n");
    });
});