How to read two files in node and check if the words exist in both

Question

I was trying out new things in node, So here I want to read two files and check if all the words in the files are the same.

Example: Two similar files where one file has some extra words added to it.

So after checking both the files, if the words of one file don't exist in the other file, then those words should be printed out

Here is what I have tried so far, But this doesn't seem to work as expected and isn't the right way

let newData = [];
let oldData = [];

(async () => {
  await new Promise(resolve => {
    fs.readFile(
      pathname.join(__dirname, "public", "hello.txt"),
      (err, data) => {
        const wordsInFile = data.toString().toLowerCase();
        // Here we should split string by some delimiter for further words processing. Assume, that your file looks like this "word1 word2". We'll use space delimiter.
        newData = wordsInFile.split(" ");
        resolve();
      }
    );
  });

  // here is the same code for the second file. Or you can move code to another function.
  await new Promise(resolve => {
    fs.readFile(pathname.join(__dirname, "public", "test.txt"), (err, data) => {
      const wordsInFile = data.toString().toLowerCase();
      // Here we should split string by some delimiter for further words processing. Assume, that your file looks like this "word1 word2". We'll use space delimiter.
      newData = wordsInFile.split(" ");
      resolve();
    });
  });
  // And now we can use Set from ES6, to find intersection/difference etc.
  const wordsNotInFileAndNotInFileTwo = new Set(
    [...newData].filter(x => !oldData.has(x))
  );
  console.log(wordsNotInFileAndNotInFileTwo);

  // But you can simple iterate two arrays to achieve your goal.
})();

Any help would be appreciated

one way, you could nest your `readFile` and do the comparison inside the nested `readFile` — 1565986223, May 01 '19 at 09:43

1565986223 · Accepted Answer · 2019-05-01T10:32:57.280

2

Nest readFile:

fs.readFile(pathname.join(__dirname, "public", "hello.txt"), (err, data) => {
  newData = data.toString().toLowerCase();
  fs.readFile(pathname.join(__dirname, "public", "test.txt"), (err, data) => {
    oldData = data.toString().toLowerCase();
    if (newData === oldData) {
      console.log("Same");
    } else {
      console.log("Not Same");
      const a = newData.split(' ')
      const b = oldData.split(' ')

      const result = a.filter(w => !oldData.includes(w));
      console.log(result.join(' '));
    }
  });
});

This way, callback in inner function has access to variables set in the outer function.

edited May 01 '19 at 10:32

answered May 01 '19 at 09:48

1565986223

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But this still doesn't show the word that isn't in the other file – Thanveer Shah May 01 '19 at 09:58
`still doesn't show the word that isn't in the other file` what do you mean? do you get any error? – 1565986223 May 01 '19 at 10:03
No error, It just prints out the entire words in the file rather than that specific word – Thanveer Shah May 01 '19 at 10:11
because that's what your logging `oldData` is the entire string in `test.txt` – 1565986223 May 01 '19 at 10:13
Yeah, So how do I print out the specific data? – Thanveer Shah May 01 '19 at 10:14
That depends, is the *different* word at the end of the string or could be anywhere in between? – 1565986223 May 01 '19 at 10:15
It could be anywhere – Thanveer Shah May 01 '19 at 10:16
Like one files has "My name is xxx" and the other files has "My name is xxx and" , then the "and" should be printed – Thanveer Shah May 01 '19 at 10:16
1

updated answer to fit what you're trying to achieve – 1565986223 May 01 '19 at 10:33
You are a god ! – Thanveer Shah May 01 '19 at 10:41

score 0 · Answer 2 · answered May 01 '19 at 09:49

The first point is asynchronous behaviour of fs.readFile function.
In short, you have to await while each file would be read. Or, at least, one of files.
Here is example with IIFE, but you can use any asynchronous function or use promises.

let newData = [];
let oldData = [];

(async() => {
  await new Promise(resolve => {
    fs.readFile(pathname.join(__dirname, "public", "hello.txt"), (err, data) => {
      const wordsInFile = data.toString().toLowerCase();
      // Here we should split string by some delimiter for further words processing. Assume, that your file looks like this "word1 word2". We'll use space delimiter.
      newData = wordsInFile.split(' ');
      resolve();
    })
  })

  // here is the same code for the second file. Or you can move code to another function.

  // And now we can use Set from ES6, to find intersection/difference etc.
  const wordsNotInFileAndNotInFileTwo = new Set([...newData].filter(x => !oldData.has(x)));
 // But you can simple iterate two arrays to achieve your goal.
})()

Here is nice article about Set.

To sum up:
First, you need to await while file would be read.
Second, you can find words difference via Set.

Sir, Why does wordsNotInFileAndNotInFileTwo print no value ? I have updated the answer with the new code — Thanveer Shah, May 01 '19 at 10:21

How to read two files in node and check if the words exist in both

2 Answers2