what is wrong with my callback?

Question

This is the file "path-info.js" that has 2 functions: pathInfo & callback. Pathinfo collects all info about file from path in the object "info", callback gets that object and returns it. Code:

"use strict";
const fs = require("fs");

let getInfo = function (err, someObject) {
    if (err) throw err;
    return someObject;
};

function pathInfo(path, callback) {
  let info = {};

  info.path = path; // write path info

  fs.stat(path, (err, type) => { // write type info
    if (type.isFile()) {
      info.type = "file";
    }
    if (type.isDirectory()) {
      info.type = "directory";
    } else {
      info.type = "undefined";
    }
  });

  fs.stat(path, (err, type) => { // write content info if it is file
    if (type.isFile()) {
      fs.readFile(path, "utf8", (err, content) => {
        info.content = content;
      });
    } else {
      info.content = "undefined";
    }
  });

  fs.stat(path, (err, type) => { // write childs if it is directory
    if (type.isDirectory()) {
      fs.readdir(path, (err, childs) => {
        info.childs = childs
      });
    } else {
      info.childs = "undefined";
    }
  });

  getInfo(null, info); // callback returns object "info"
}

module.exports = pathInfo;

I use my callback function as it was shown, for instance, here: nodeJs callbacks simple example. Still, this code does not work and I do not why.

I call this code using file "test.js", here is the code:

const pathInfo = require('./path-info');
function showInfo(err, info) {
  if (err) {
    console.log('Error occurred');
    return;
  }

  switch (info.type) {
    case 'file':
      console.log(`${info.path} — is File, contents:`);
      console.log(info.content);
      console.log('-'.repeat(10));
      break;
    case 'directory':
      console.log(`${info.path} — is Directory, child files:`);
      info.childs.forEach(name => console.log(`  ${name}`));
      console.log('-'.repeat(10));
      break;
    default:
      console.log('Is not supported');
      break;
  }
}

pathInfo(__dirname, showInfo);
pathInfo(__filename, showInfo);

So the logic is that I need to give my callback the object that contains some info about directory or file. Depending on that, some console.logs will be displayed.

Any help will be appreciated!

UPD: updated the code, just renamed my "callback" function to "getInfo".

Answer 1

A callback is a function you pass as parameter to another function.

In your case, your second parameter is function showInfo which is your callback. Your function pathInfo accepts two parameters, second is showInfo.

So when you call it, you execute code within showInfo with some parameters, usually err, then something else.

In your case, you name second parameter "callback" in showInfo, so you have to execute it with asked parameters (err and info).

Example:

function myfunc (parameter,cb) {
    cb(null,{});
}

myfunc("one", function (err,res) {
    console.log(err);
});

where "cb" in "myfunc" is function sent as second parameter.

It can be write like this as you did it:

var cb = function (err,res) {
    console.log(err);
}

myfunc("one",cb);

Answer 2

In case anyone is interested.. I found a solution and it works! As @ADreNaLiNe-DJ correctly stated, my callbacks are not finished when i call getInfo callback to return info object. So the way out is to change my level of abstraction: all i´ve done is pasted my callbacks inside functions. See that code:

"use strict";
const fs = require("fs");

let pathInfo = (path, callback) => {
  let info = {};
  info.path = path;

  fs.stat(path, (err, type) => {
    if (err) throw err;
    if (type.isFile()) {
      info.type = "file";
      fs.readFile(path, "utf8", (err, content) => {
        info.content = content;
        info.childs = undefined;
        callback(err, info);
      });
    }
    if (type.isDirectory()) {
      info.type = "directory";
      fs.readdir(path, (err, childs) => {
        info.childs = childs;
        info.content = undefined;
        callback(err, info);
      });
    }
  });
};

let showInfo = (err, info) => {     // Отсюда и ниже вставлен код из текста
  if (err) {                        // из домашнего задания
    console.log('Возникла ошибка при получении информации');
    return;
  }

  switch (info.type) {
    case 'file':
      console.log(`${info.path} — является файлом, содержимое:`);
      console.log(info.content);
      console.log('-'.repeat(10));
      break;
    case 'directory':
      console.log(`${info.path} — является папкой, список файлов и папок в ней:`);
      info.childs.forEach(name => console.log(`  ${name}`));
      console.log('-'.repeat(10));
      break;
    default:
      console.log('Данный тип узла не поддерживается');
      break;
  }
};

pathInfo(__dirname, showInfo);
pathInfo(__filename, showInfo);

PS: sorry for Russian console.logs, hope it won't disturb you (they don't bring any value anyway into understanding how it works)