How to use the file.join function in file

Application.prototype.findJakefileLocation = function() {
    var directory = FILE.cwd();
    var filename = null;

    while (!(filename = this.hasJakefile(directory)) && directory !== "/")// && !this._options.nosearch)
        directory = FILE.absolute(FILE.join(directory, ".."));

    if (!filename)
        return null;

    return [filename, directory];
}

ApplicationTask.prototype.defineCacheManifestTask = function()
{
    if (!this.shouldGenerateCacheManifest())
        return;

    var productPath = FILE.join(this.buildProductPath(), "");
    var indexFilePath = this.buildIndexFilePath();

    // TODO: can we conditionally generate based on outdated files?
    var manifestPath = FILE.join(productPath, "app.manifest");
    Jake.task(manifestPath, function() {
        require("../cache-manifest").generateManifest(productPath, { index : indexFilePath });
    });

    this.enhance([manifestPath]);
}

CFPropertyList.modifyPlist(buildNative.join("Contents", "Info.plist"), function(plist) {

        plist.setValueForKey("CFBundleName", defaultBundleName);
        plist.setValueForKey("NHInitialResource", FILE.join(rootBaseName, options.index));

        // merge Cappuccino plist
        var cappPlistPath = rootPath.join("Info.plist");
        if (cappPlistPath.isFile())
            mergePlist(plist, cappPlistPath);

        if (options.extraPlistPath)
            mergePlist(plist, options.extraPlistPath);
    });
}

RouterLoader.prototype.loadInto = function(app) {
    var routerFiles = this.list();
    for (var i=0;i

function initOutputDir(){
	if (writeFlag){
		var dirPath = file.join(profilePath, "testResults");
		if (!file.exists(dirPath)) file.mkpath(dirPath);
		var existingFiles = file.list(dirPath);
		var i = 0;
		for (i = 0; i < existingFiles.length; i++)
		{
			file.remove(file.join(dirPath,existingFiles[i]));
		}
	}
}