Question

I am trying to set a variable value at an object (class) level from deep inside a few levels of nested anonymous javascript method calls. How do I do this?

Here is some code to explain what I am trying to do. Disclaimer: I am not that comfortable with the concept of closures in javascript, so I might be going along a wrong path here. Any suggestion about a succinct way to achieve what I want to do would be greatly appreciated.

// FileUtils object.
var FileUtils = function () {
    // Member variables.
    this.ConfRootDir = null;
};

// Method to get a file entry.
// successCallback has to be a method with a FileEntry object.
FileUtils.prototype.getFileEntry = function (fileName, successCallback) {
    if (this.ConfRootDir == null) {
        var thisObj = this;
        // Request the root filesystem 
            // [** 1st callback, using anon method]
        window.requestFileSystem(LocalFileSystem.PERSISTENT, 0,
            function (fileSystem) {                        
                // Get the root directory of the file system.
                var rootDir = fileSystem.root;
                // Get the ConferenceToGo directory, or create if required.
                // [** 2nd callback, using anon method]
                rootDir.getDirectory("ConferenceToGo", { create: true, exclusive: false },
                    function (confDir) {
                        // Set values for future use 
                        // [** Definitely wrong scoping. The class level variable 
                        // can't be accessed using 'this'. What to do? **]
                        this.ConfRootDir = confDir;
                        // Now try getting the handle for the list file.
                        //  [** 3rd callback, using anon method. Irrelevant at this point.]
                        this.ConfRootDir.getFile(fileName, { create: false },
                            successCallback, // Success callback [getFile]
                            function (error) {
                                logError("Unable to retrieve file: ", true, true, error);
                            }); // Failure callback [getFile]
                    }, // Success callback [getDirectory]
                    function (error) { logError("Unable to create new directory: ", true, true, error); }); // Failure callback [getDirectory]
            }, // Success callback [requestFileSystem]
            function (error) { logError("Problem reading file system: ", true, true, error); }
        );
    }
}

I know that the scoping (by using ‘this’) is all wrong in the above piece of code, but not sure how to get it right. I have seen a few answers about binding to context (like this one), but I am using anonymous methods so that makes it harder. Note: Although I show only one method in the prototype of FileUtils here, there a few more.

Those who are aware can probably recognize that I am using methods from the cordova (PhoneGap) library for cross-platform mobile dev in HTML5 and JS, but that is not really much relevant here.

Answer 1

… function() { function() { function() { …
                    // Set values for future use 
                    // [** Definitely wrong scoping. The class level variable 
                    // can't be accessed using 'this'. What to do? **]
                    this.ConfRootDir = confDir;

You already have preparated the answer: thisObj.ConfRootDir. The thisObj variable is available in the scope of the nested function, and still points to the this keyword of the outer getFileEntry function, i.e. to the FileUtils instance.