Reading and writing files (JSON) using node.js

Question

I have a function that should read a JSON file and update this file (writeFile). When I call this function 2 times or more it doesn't update my file and after the 1st call it's adding 1/2 curling brackets at the end of my JSON file. Here is my function:

var fs = require('fs');

function updateJson(ticker, value) {
    //var stocksJson = JSON.parse(fs.readFileSync("stocktest.json"));
    fs.readFile('stocktest.json', function(error, file) {
        var stocksJson =  JSON.parse(file);



        if (stocksJson[ticker]!=null) {
            console.log(ticker+" price : " + stocksJson[ticker].price);
            console.log("changing the value...")
            stocksJson[ticker].price =  value;
            console.log("Price after the change has been made -- " + stocksJson[ticker].price);
            console.log("printing the the Json.stringify")
            console.log(JSON.stringify(stocksJson, null, 4));
             fs.writeFile('stocktest.json',JSON.stringify(stocksJson, null, 4) , function(err) {  
                            if(!err) {
                                console.log("File successfully written");
                            }
                            if (err) {
                                console.error(err);
                            }

                       });
        }
        else {
            console.log(ticker + " doesn't exist on the json");
        }
    });
} // end of updateJson

updateJson("IBM", 77);
updateJson("AAPL", 88);

This is my original JSON file (before this function was executed):

{
    "NVDA": {
        "name": "Nvidia Corporation",
        "symbol": "NVDA",
        "logo": "nvidia.png",
        "price": 0,
        "prod": "Nvidia Corporation, gforce, g-force, shield"
    },
    "AAPL": {
        "name": "Apple inc",
        "symbol": "AAPL",
        "logo": "apple.png",
        "price": 0,
        "prod": "Apple inc, mac, macbook, iphone, ipod, ipad, osx"
    },
    "GOOG": {
        "name": "Google inc",
        "symbol": "GOOG",
        "logo": "google.png",
        "price": 0,
        "prod": "search, android, glass, drive, code school"
    },
    "IBM": {
        "name": "ibm",
        "symbol": "ibm",
        "logo": "google.png",
        "price": 0,
        "prod": "search, android, glass, drive, code school"
    }
}

This is the the part where i'm using the updateJson function:

MongoClient.connect("mongodb://" + host + ":" + port + "/" + dbName, function (error, db){

    console.log("Connection is opened to : " + "mongodb://" + host + ":" + port + "/" + dbName);

    var q = async.queue(function (doc, callback) {
  // code for your update

            var stockName = doc.ticker;
            var stockValue =  doc.value;

            var yUrl = "http://finance.yahoo.com/q/ks?s=" + stockName;
            console.log("The url is : " + yUrl);
            getStockValue(stockName, yUrl, callback, db);
            // insert here the update of the json
            updateJson(stockName, stockValue);
    }, Infinity);

var cursor = db.collection(requiredCollection).find();
cursor.each(function(err, doc) {
  if (err) throw err;
  if(doc!=null) {
  q.push(doc); // dispatching doc to async.queue
} 
});

q.drain = function() {
  if (cursor.isClosed()) {
    console.log('all items have been processed');
    db.close();
  }
}

 }); // end of connection to MongoClien

000 · Accepted Answer · 2014-09-05 17:18:09Z

3

You need to add a callback to your updateJson function, so that

updateJson("IBM", 77);
updateJson("AAPL", 88);

turns into:

updateJson("IBM", 77, function() {
    updateJson("AAPL", 88);
});

function updateJson(ticker, value, callback) {
    //var stocksJson = JSON.parse(fs.readFileSync("stocktest.json"));
    fs.readFile('stocktest.json', function(error, file) {
        var stocksJson =  JSON.parse(file);



        if (stocksJson[ticker]!=null) {
            console.log(ticker+" price : " + stocksJson[ticker].price);
            console.log("changing the value...")
            stocksJson[ticker].price =  value;
            console.log("Price after the change has been made -- " + stocksJson[ticker].price);
            console.log("printing the the Json.stringify")
            console.log(JSON.stringify(stocksJson, null, 4));
             fs.writeFile('stocktest.json',JSON.stringify(stocksJson, null, 4) , function(err) {  
                            if(!err) {
                                console.log("File successfully written");
                            }
                            if (err) {
                                console.error(err);
                            }
                            callback();

                       });
        }
        else {
            console.log(ticker + " doesn't exist on the json");
        }
    });
} // end of updaJson

I recommend using the async library for this: https://github.com/caolan/async#eachSeries

function updateJson(data, callback) {
    var ticker = data.ticker;
    var value = data.value;
    //var stocksJson = JSON.parse(fs.readFileSync("stocktest.json"));
    fs.readFile('stocktest.json', function(error, file) {
        if (error) {
            callback(error);
        }
        var stocksJson =  JSON.parse(file);

        if (stocksJson[ticker]!=null) {
            console.log(ticker+" price : " + stocksJson[ticker].price);
            console.log("changing the value...")
            stocksJson[ticker].price =  value;
            console.log("Price after the change has been made -- " + stocksJson[ticker].price);
            console.log("printing the the Json.stringify")
            console.log(JSON.stringify(stocksJson, null, 4));
             fs.writeFile('stocktest.json',JSON.stringify(stocksJson, null, 4) , function(err) {  
                            if(!err) {
                                callback(null, "File successfully written");
                            }
                            if (err) {
                                callback(err);
                            }

                       });
        }
        else {
            callback(ticker + " doesn't exist on the json");
        }
    });
} // end of updaJson

async.eachSeries([
  {ticker:"IBM", value:77},
  {ticker:"AAPL", value:88}
], updateJson, function(err, success) {
  console.log(err, success);
});

edited Sep 5, 2014 at 17:18

answered Sep 5, 2014 at 16:35

000

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9 Comments

Alex Brodov Over a year ago

I've tried the first option and i'm getting this error: callback(); TypeError: undefined is not a function

000 Over a year ago

That's because the second function call (updateJson("AAPL", 88);) is not passing a callback. Try this: updateJson("AAPL", 88, function() { console.log('hey it worked'); });

Alex Brodov Over a year ago

Ok the 2nd one is working, lets say that i don't know how many times i'll need to call this function it depends on my other functions, because i'm getting some live data from some server , there is any option to call this function in a different way, i mean i don't know if it will be 5 / 10 / 15 times so i can't write it like this ..

000 Over a year ago

Use this library. github.com/caolan/async. You're interested in the "series" method

Alex Brodov Over a year ago

I can't see the example that you wrote for eachSeries

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