Node.js fs.readdir、fs.stat

Question

我正在学习一些教程，但无法理解为什么这一行“self.only_dirs.push(files[i]);”导致有关它“未定义”的错误。这肯定是一个变量范围问题，但我尝试过的都没有成功。我需要如何声明变量以便这些嵌入的回调函数能够识别它们？

function load_album_list(callback, callback2)
{
	var self = this;
	fs.readdir
	(
		'albums',
		function (err, files)
		{
			if(err)
			{
				callback(err, null);
				return;
			}
			
			var only_dirs = [];
			var remaining = files.length;
			for (var i = 0; i < files.length; i++)
			{

				fs.stat("albums/" + files[i],
						function(err, stats)
						{
							if(stats.isDirectory())
							{
								self.only_dirs.push(files[i]);
							}
							console.log("remaining: " + self.remaining);
							self.remaining -= 1;
							if (self.remaining == 0)
								callback(null, self.only_dirs);	
						}
					);

			}
			
			callback(null, only_dirs);
		}
	);
}

Answer 1

function load_album_list(callback, callback2)
{
	var self = this;
    self.only_dirs = []; //<----- declare only_dirs in this scope
	fs.readdir
	(
		'albums',
		function (err, files)
		{
			if(err)
			{
				callback(err, null);
				return;
			}
			
			//var only_dirs = []; <--- remove this reference
			var remaining = files.length;
			for (var i = 0; i < files.length; i++)
			{

				fs.stat("albums/" + files[i],
						function(err, stats)
						{
							if(stats.isDirectory())
							{
								self.only_dirs.push(files[i]);
							}
							console.log("remaining: " + self.remaining);
							self.remaining -= 1;
							if (self.remaining == 0)
								callback(null, self.only_dirs);	
						}
					);

			}
			
			callback(null, self.only_dirs);
		}
	);
}