NodeJS need to concatenate JSON using custom structure

Question

Hi I am trying to create a JSON file using all the JSON files in a particular directory. I want it to be updated any time I add a new file to the directory. So, I am writing the code for this in the 'post' part of my file upload page. I have the following code:

    for (i = 0; i < files; i++) {
        console.log('Entered For loop');
        console.log('Count:', count);
        console.log('Count:', sensor);
        fs.readFile('/uploads/' + bbbid + '/device'+count+ '.json' , 'utf8', function (err, data) {
            if (err) throw err; // we'll not consider error handling for now
            var obj = JSON.parse(data);
            JSON.stringify(obj);
            //console.log(myfiles[i]);
            var ddl = require('/uploads/' + bbbid + '/device' +sensor+ '.json');
            //var ddl = require('/uploads/' + bbbid + '/device' + count + '.json');
            cddl = cddl + ", {" + obj.DDL.Sensor.Description.Verbose_Description + ":" + JSON.stringify(ddl) + "}"
            JSON.stringify(cddl);
            console.log(cddl);
            count++;
            sensor++;
            console.log('Count:', count);
            console.log('Sensor:', sensor);
        });

    }

I have initialized count and sensor to 1 before the post method begins. The output I get:

    Entered For loop
    Count: 2
    Count: 2
    Entered For loop
    Count: 2
    Count: 2

Can we not use fs.readFile in the for loop? I think my loop exits before going in the readfile function. Help please!

You are using an asynchronous file reading, try with readFileSync (nodejs.org/api/fs.html#fs_fs_readfilesync_file_options) — angrykoala
– angrykoala, Commented Nov 25, 2016 at 14:45

Mykola Borysyuk · Accepted Answer · 2016-11-25 14:57:52Z

2

For loop is sync and fs.ReadFile async. Your assumption is correct.

You need to use

https://nodejs.org/api/fs.html#fs_fs_readfilesync_file_options

Here is the example

var fs = require('fs');

var contents = fs.readFileSync('package.json');

console.log(JSON.parse(contents));

Hope this helps.

edited Nov 25, 2016 at 14:57

answered Nov 25, 2016 at 14:44

Mykola Borysyuk

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5 Comments

Mykola Borysyuk Over a year ago

Well you need to add error handling as readFileSync will throw exceptions. But everything else looks ok.

Mykola Borysyuk Over a year ago

code.runnable.com/VVPFREu0oblSpIch/read-file-sync-for-node-js Also make sure you wrap all in try/catch block. And you should be fine.

user7201227 Over a year ago

I want to parse that data. How do I do that?

Mykola Borysyuk Over a year ago

Check my answer. I give you example

Daphoque Over a year ago

var data = fs.readFileSync('/uploads/' + bbbid + '/device'+count+ '.json' , 'utf8');

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