这也可以:

fs.readFile(`${__dirname}/../../foo.bar`);

如果你不确定父结点在哪里，这个会给你路径;

var path = require('path'),
    __parentDir = path.dirname(module.parent.filename);

fs.readFile(__parentDir + '/foo.bar');

你可以使用

path.join(__dirname, '../..');

试试这个:

fs.readFile(__dirname + '/../../foo.bar');

请注意相对路径开头的正斜杠。

你可以用不同的方法定位父文件夹下的文件，

const path = require('path');
const fs = require('fs');

// reads foo.bar file which is located in immediate parent folder.
fs.readFile(path.join(__dirname, '..', 'foo.bar'); 

// Method 1: reads foo.bar file which is located in 2 level back of the current folder.
path.join(__dirname, '..','..');


// Method 2: reads foo.bar file which is located in 2 level back of the current folder.
fs.readFile(path.normalize(__dirname + "/../../foo.bar"));

// Method 3: reads foo.bar file which is located in 2 level back of the current folder.
fs.readFile(__dirname + '/../../foo.bar');

// Method 4: reads foo.bar file which is located in 2 level back of the current folder.
fs.readFile(path.resolve(__dirname, '..', '..','foo.bar'));

我知道这有点挑剔，但到目前为止，所有的答案都不太正确。

path.join()的目的是消除调用者知道使用哪个目录分隔符的需要(使代码与平台无关)。

从技术上讲，正确答案应该是这样的:

var path = require("path");

fs.readFile(path.join(__dirname, '..', '..', 'foo.bar'));

我本想把这句话作为对Alex Wayne的回答的评论，但还不够代表!

编辑:根据用户1767586的观察