Looping through json data in express.js

Question

Im trying to loop through a json file and pick out every episode, but I'm confused that my loop only output the first current_episode, much appreciated if anyone can check my problem!

app.get('/episodes', function(req, res){
    fs.readFile('channels.json', 'utf8', function (err, data) {
        var jsondata = JSON.parse(data);
        for (var i=0; i<jsondata.channels.length; i++){
            var myChannel = jsondata.channels[i].current_episode;
            res.send(myChannel);
        }
    })
});

My json data:

{
  "total": 70,
  "request_uri": "\/channels\/",
  "channels": [
    {
      "channel_id": 42,
      "current_episode": [
        {
          "id": 126248,
          "title": "Spanarna",
        }
      ]
    },
    {
      "channel_id": 43,
      "current_episode": [
        {
          "id": 126255,
          "title": "Beck: I stormens \u00f6ga",
        }
      ]
    },
............
}

JohnnyHK · Accepted Answer · 2012-11-16 14:35:24Z

7

res.send writes the data and ends the request. Try this instead:

app.get('/episodes', function(req, res){
    fs.readFile('channels.json', 'utf8', function (err, data) {
        var jsondata = JSON.parse(data);
        res.writeHead(200, {'Content-Type': 'text/plain'});
        for (var i=0; i<jsondata.channels.length; i++){
            var myChannel = jsondata.channels[i].current_episode;
            res.write(JSON.stringify(myChannel));
        }
        res.end();
    })
});

edited Nov 16, 2012 at 14:35

answered Nov 16, 2012 at 14:23

JohnnyHK

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4 Comments

nihulus Over a year ago

got error TypeError: first argument must be a string or Buffer

JohnnyHK Over a year ago

@nihulus If myChannel isn't a string you need to convert it to one. Simplest would be JSON.stringify(myChannel)

JohnnyHK Over a year ago

@nihulus If title is a property of current_episode, that's how you'd do it.

JohnnyHK Over a year ago

@nihulus Then current_episode in this case must be null. Log it to the console to help debug it.

jcreamer898 · Accepted Answer · 2012-11-16 14:24:11Z

2

Try building a string of your episodes.

app.get('/episodes', function(req, res){
    fs.readFile('channels.json', 'utf8', function (err, data) {
        var jsondata = JSON.parse(data),
            myChannel = [];
        for (var i=0; i<jsondata.channels.length; i++){
            myChannel.push( jsondata.channels[i].current_episode );
        }
        res.send( myChannel.join("\n") );
    })
});

answered Nov 16, 2012 at 14:24

jcreamer898

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2 Comments

nihulus Over a year ago

i got a output all data is object [object object]

jcreamer898 Over a year ago

Oops, yea you'd need to do have another loop to loop over the current_episode since it's also an array based on your structure.

Hector Correa · Accepted Answer · 2012-11-16 14:30:01Z

1

Because you have res.send(myChannel) inside the loop. res.send is sending the first channel as it finds and ignores the next calls to res.send().

Instead of this you should concatenate all the channels into a string and issue a res.send(allChannels) outside the loop.

answered Nov 16, 2012 at 14:30

Hector Correa

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Comments

Community · Accepted Answer · 2017-05-23 10:26:43Z

0

Easiest way I found was:

You could try the following, however it will also load all the keys into memory

Object.keys(o).forEach(function(key, index, originalObject) {
  var val = o[key];
  logic();
});

However since Object.keys is a native method it may allow for better optimisation.

Whilst this was the code I would have always done I found this here (slightly more transparent code) whilst checking if this was the most optimal way to do things: Iterate over object keys in node.js

edited May 23, 2017 at 10:26

CommunityBot

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answered Jun 23, 2015 at 22:39

Jamie Hutber

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Comments

JKV · Accepted Answer · 2014-04-29 07:46:46Z

function search_items( args ) { 
if ( args ) {       
    string = args.toLowerCase().replace(/"/g, "").replace(/'/g, "").split(" ");
    for ( var i=0, j=0; i<string.length; i++ ) {        
    (function(i){           

        vocabulary.findOne({word:string[i]}, function(error, search){ // find vocabulary info

        if ( !error && search ) {
j++;
        pages.findOne({voc_id:ObjectID(search._id)}, function(error, pages){ // find pages info

            if ( !error && pages ) {

            page_tokens.findOne({page_id:ObjectID(pages._id), voc_id:ObjectID(search._id)}, function(error, page_token){ // find page tokens info

                if ( !error && page_token ) {

                pos_tags.findOne({_id:ObjectID(page_token.pos_tag_id)}, function(error, pos_tag){ // find pos_tags info

                    if ( !error && pos_tag ) {

                    resultTotal.push({vocabulary:search.word, pages:{doc:pages.base_url+pages.path}, page_tokens:{sentence_number:page_token.sentance_number,token_position: page_token.token_position}, pos_tags: { tag:pos_tag.tag } });
                    j--;
                    console.log(j);
                    if ( j==0 ) {

                        res.json({success:resultTotal});

                    }

                    } else {
                    res.json({ error:true });                       
                    }           

                });

                } 

            });             
            }           
        });         
        }           
    });     
    })(i)       
    }
} 
}

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