Exercise - Work with paths

5 minutes

The Node.js path module and __dirname global variable are two ways to define and compose file system paths.

In the previous exercise, you wrote a program that iterates through a folder to find any of the sales.json files inside.

In this exercise, you'll use the path module and __dirname global variable to improve the program so that it will find any file with a .json extension.

Include the path module

At the top of the index.js file, include the path module.

const path = require("path");

Use the current directory

In the current index.js code, you're passing the static location of the stores folder. We'll change that code to use the __dirname value instead of passing a static folder name.

In the main method, create a variable to store a path to the stores directory by using the __dirname constant.

async function main() {
  const salesDir = path.join(__dirname, "stores");

  const salesFiles = await findSalesFiles(salesDir);
  console.log(salesFiles);
}

Press Ctrl+S or Cmd+S to save the file.

Run the program from the command line.

node index.js

Notice that the path that's now listed for the files is the full system path. This is because the __dirname constant returns the full path to the current location.

[
  '/home/username/node-files/stores/201/sales.json',
  '/home/username/node-files/stores/202/sales.json',
  '/home/username/node-files/stores/203/sales.json',
  '/home/username/node-files/stores/204/sales.json',
]

Join paths

Instead of concatenating folder names to make a new path to search, you'll change the code to use the path.join method. This code will then work across operating systems.

Change the findFiles method to use path.join.

// search this directory for files (this is recursion!)
await findFiles(path.join(folderName, item.name));

Press Ctrl+S or Cmd+S to save the file.
Run the program from the command line.
```
node index.js
```
The output will be the same as the previous step, but the program is now more robust because it uses path.join instead of concatenating strings.

Find all .json files

Instead of looking for just sales.json files, the program needs to search for any file with an extension of .json. To do that, use the path.extname method to check the filename extension.

Run the following command in the terminal to rename the stores/201/sales.json file to stores/sales/totals.json.
```
mv stores/201/sales.json stores/201/totals.json
```

In the findFiles method, change the if statement to check just the filename extension. Use the path.join method to compose the full path to the file.

if (path.extname(item.name) === ".json") {
  // store the file path in the salesFiles array
  await salesFiles.push(path.join(folderName, item.name));
}

Press Ctrl+S or Cmd+S to save the file.

Run the program from the command line.

node index.js

The output now shows all the .json files in any of the store ID directories.

[
   '/home/username/node-files/stores/201/totals.json',
   '/home/username/node-files/stores/202/sales.json',
   '/home/username/node-files/stores/203/sales.json',
   '/home/username/node-files/stores/204/sales.json'
]

Great job! You've used the path module and the __dirname constant to make the program much more robust. In the next section, you'll learn how to create directories and move files between locations.

Got stuck?

If you got stuck at any point in this exercise, here's the completed code. Remove everything in index.js and replace it with this solution.

const fs = require("fs").promises;
const path = require("path");

async function findSalesFiles(folderName) {
  // this array will hold sales files as they are found
  let salesFiles = [];

  async function findFiles(folderName) {
    // read all the items in the current folder
    const items = await fs.readdir(folderName, { withFileTypes: true });

    // iterate over each found item
    for (item of items) {
      // if the item is a directory, it will need to be searched
      if (item.isDirectory()) {
        // call this method recursively, appending the folder name to make a new path
        await findFiles(path.join(folderName, item.name));
      } else {
        // Make sure the discovered file is a .json file
        if (path.extname(item.name) === ".json") {
          // store the file path in the salesFiles array
          salesFiles.push(path.join(folderName, item.name));
        }
      }
    }
  }

  await findFiles(folderName);

  return salesFiles;
}

async function main() {
  const salesDir = path.join(__dirname, "stores");

  // find paths to all the sales files
  const salesFiles = await findSalesFiles(salesDir);
  console.log(salesFiles);
}

main();

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