Why is fs.readFile returning a buffer?

Question

I have referred to this question already. That is, I don't believe my problem lies in a misunderstanding of async.

Here is the relevant part of my module.

var fs = require('fs');
var q = require('q');
var u = require('../utils/json');

var indexFile = './data/index.json';

function getIndex() {
    var def = q.defer(),
        promise = def.promise,
        obj;

    fs.readFile(indexFile, function(err,data) {
        if (err) {
            throw err;
            def.reject(err);
        }
        console.log('data', data);

        def.resolve(obj);
    });

    return promise;
}

When I log 'data', I'm getting a buffer (below), rather than the JSON content of that file.

<Buffer 5b 7b 22 68 65 6c 6c 6f 22 3a 22 77 6f 72 6c 64 22 7d 5d>

Any thoughts on why?

as an aside, don't throw `err` if you want to reject your deferred with it. — Andbdrew, Oct 09 '14 at 02:19
And the reason the API defaults to a buffer instead of a string is that buffers are the only safe way of reading binary data. But you can convert a buffer to a string even after reading it by either calling `.toString()` directly of appending forcing it into a string context: `'' + buffer` — slebetman, Oct 09 '14 at 03:44

score 17 · Accepted Answer · answered Oct 09 '14 at 02:17

17

As per the Node.js API docs for 'fs' module, if the encoding option isn't passed, the read functions will return a buffer.

If you pass a value for encoding, it will return a string with that encoding:

fs.readFile('/etc/passwd', 'utf-8', callback)

answered Oct 09 '14 at 02:17

aarosil

4,848
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score 2 · Answer 2 · edited Sep 30 '16 at 07:51

2

As stated before, fs module requires the encoding option as second parameter.

Also, if you are sure that your file consists utf-8 string, you can use;

fs.readFile(indexFile, function(err,data) {
    if (err) {
        return def.reject(err);
    }

    console.log('data', data.toString());

    def.resolve(obj);
});

edited Sep 30 '16 at 07:51

Dan D.

73,243
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answered Sep 30 '16 at 07:48

Kartal

424
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score 1 · Answer 3 · answered Dec 02 '15 at 14:56

1

Try this... You need to include encoding

fs.readFile(indexFile,'utf8', function(err,data) {
    if (err) {
        throw err;
    }
    //Do something with data
    console.log(data);
});

answered Dec 02 '15 at 14:56

T M

516
5
18

Why is fs.readFile returning a buffer?

3 Answers3