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Exercise - Work with paths

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As a developer at Tailwind Traders, you're about to enhance a program by using the Node.js path module and __dirname global variable. This will allow the program to dynamically locate and process any .json files, regardless of where the program is run from.

Include the path module

At the top of your existing 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. Let's change that code to use the __dirname value instead of passing a static folder name.

1. 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);
   }
   

2. 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, because the __dirname constant returns the full path to the current location.

   [
      '/workspaces/node-essentials/nodejs-files/stores/201/sales.json',
      '/workspaces/node-essentials/nodejs-files/stores/202/sales.json',
      '/workspaces/node-essentials/nodejs-files/stores/203/sales.json',
      '/workspaces/node-essentials/nodejs-files/stores/204/sales.json'
   ]
   

Join paths

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

1. Change the findFiles method to use path.join.

   // previous code - with string concatentation
   const resultsReturned = await findSalesFiles(`${folderName}/${item.name}`);
   
   // current code - with path.join
   const resultsReturned = await findSalesFiles(path.join(folderName,item.name));
   

2. Run the program from the command line.

   node index.js
   

   The output is 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.

1. 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
   

2. In the findSalesFiles function, change the if statement to check just the filename extension.

   if (path.extname(item.name) === ".json") {
     results.push(`${folderName}/${item.name}`);
   }
   

3. 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-essentials/nodejs-files/stores/201/totals.json',
      '/home/username/node-essentials/nodejs-files/stores/202/sales.json',
      '/home/username/node-essentials/nodejs-files/stores/203/sales.json',
      '/home/username/node-essentials/nodejs-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) {

  // (1) Add an array at the top, to hold the paths to all the sales files that the program finds.
  let results = [];

  // (2) Read the currentFolder with the `readdir` method. 
  const items = await fs.readdir(folderName, { withFileTypes: true });

  // (3) Add a block to loop over each item returned from the `readdir` method using the asynchronous `for...of` loop. 
  for (const item of items) {

    // (4) Add an `if` statement to determine if the item is a file or a directory. 
    if (item.isDirectory()) {

      // (5) If the item is a directory,  recursively call the function `findSalesFiles` again, passing in the path to the item. 
      const resultsReturned = await findSalesFiles(path.join(folderName, item.name));
      results = results.concat(resultsReturned);
    } else {
      // (6) If it's not a directory, add a check to make sure the item name matches *sales.json*.
      if (path.extname(item.name) === ".json")
        results.push(`${folderName}/${item.name}`);
    }
  }


  return results;
}

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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