CODEWITHSUNDEEP
javascriptnode.js
user1207289
user1207289

Reputation: 3273

node - fs - reading two files so they can be compared

How can I read two file using fs and have both result available in a way , where I can compare them. I looked at this but its slightly different and I couldnt find a way to do what I need.

I can call the diffChars from callback, but how to do with two callback functions?

  fs.readFile('/abc1.txt',  function (err, data1) {
    console.log(data1);
});
  fs.readFile('/abc1.txt',  function (err, data2) {
    console.log(data2);
});

 later I want to do like this

 var fileDiff = require("diff");
 var difference = fileDiff.diffChars(data1,data2);
 cnsole.log(difference);

note: I am restrictive on libraries I can use because of npm proxy repository

Upvotes: 1

Views: 3073

Answers (3)

pr0p
pr0p

Reputation: 2358

Node uses asynchronous style of coding. So when you are reading file one the 2nd file is also being read and also the next code is being executed. Thus you can use promises or callbacks. Here is one solution

fs.readFile('/abc1.txt',  function (err, data1) {
    console.log(data1);
    fs.readFile('/abc1.txt',  function (err, data2) {
        console.log(data2);
        var fileDiff = require("diff");
        var difference = fileDiff.diffChars(data1,data2);
        console.log(difference);
    });      
});

or use promises like

var data;
fs.readFile('/abc1.txt')
.then((data1)=>{
    data = data1;
    return(fs.readFile('/abc1.txt'))
})
.then((data2)=>{
    var difference = fileDiff.diffChars(data1,data2);
    return(difference)
})
/* do what ever you want here*/
.catch((err)=>{throw err;})

Upvotes: 0

Moritz Schmitz v. Hülst
Moritz Schmitz v. Hülst

Reputation: 3682

You don't need the callback functions. You could use fs.readFileSync().

EDIT However, fs.readFileSync() is blocking and the next line will only be executed once the function returns.

If you insist on using callbacks:

fs.readFile("abc123.txt", (error1, data1) => {
  if (error1) {
    return;
  }

  fs.readFile("abc456.txt", (error2, data2) => {
    if (error2) {
      return;
    }

    console.log(data1 === data2);
  });
});

Upvotes: 1

Daniel A. White
Daniel A. White

Reputation: 191058

This is a perfect case for a Promise and Promise.all.

function readFile(name) {
    return new Promise((resolve, reject) =>
        fs.readFile(name,  function (err, data) {
            if (err) { reject(err); }
            resolve(data);
        });
    });
}

Promise.all(readFile('file1'), readFile('file2')).then(data => {
   var file1 = data[0];
   var file2 = data[1];
});

Upvotes: 6

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