Node.JS JSON.parse error undefined

Question

I tried to parse json file in node but there always error and I google it but cannot solve it . Can you help me?

undefined:1
undefined
^
SyntaxError: Unexpected token u
at Object.parse (native)
at Object.<anonymous> (app.js:13:19)
at Module._compile (module.js:449:26)
at Object.Module._extensions..js (module.js:467:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.runMain (module.js:492:10)
at process.startup.processNextTick.process._tickCallback (node.js:244:9)

this's my code

var app = express();
var mongodb = require("mongoskin");
var fs = require('fs');

var content;
fs.readFile('./config/db.json', function read(err, data) {
    if (err) {
        throw err;
    }
    content = data;
});
var config = JSON.parse(content);


app.get('/', function(req, res){
    res.send(config.left);
});

app.listen(process.env.VCAP_APP_PORT || 3000);

and the db.json is this. As you can see, there are no errors.

{
  "left": 3
}

Answer 1

readFile is asynchronous, so your JSON.parse line is called before you assign a value to content, and so content has its default value of undefined.

You have two options:

1. Move the logic using the data into the callback.

   var app = express();
   var mongodb = require("mongoskin");
   var fs = require('fs');
   
   fs.readFile('./config/db.json', function read(err, data) {
       if (err) {
           throw err;
       }
   
       var config = JSON.parse(data); // <=== Note I'm using `data`, not `content`; we don't need a `content` variable anymore
   
       app.get('/', function(req, res){
           res.send(config.left);
       });
   
       app.listen(process.env.VCAP_APP_PORT || 3000);
   });
   

2. Use the synchronous version of readFile (which is readFileSync).

   // ...
   content = fs.readFileSync('./config/db.json');
   
   var config = JSON.parse(content);
   // ...