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Node.JS JSON.parse error undefined

I tried to parse the json file in node but there is always an error and I google, but I can not 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 is 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 db.json is this. As you can see, there are no errors.

{
  "left": 3
}
+5
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2 answers

readFileis asynchronous, so your line JSON.parseis called before you assign a value content, and therefore contenthas a default value undefined.

You have two options:

  • Move the logic using the data to 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);
});

  • Use the synchronous version readFile(which readFileSync).

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

var config = JSON.parse(content);
// ...
+6
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content undefined, . JSON readFile readFileSync .

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, , node.js, this

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