在Node.js中顺序解析JSON

Question

I'm trying to parse some JSON in Node.js. The JSON comes from a .json file. I think I'm missing something due to Node's asynchronous nature. However, I'm not sure how to get beyond it. Currently, I'm trying the following code:

var results = null;

// Read the .json file
var file = __dirname + '/config.json';
fs.readFile(file, 'utf8', function (err, data) {
  if (err) {
    return;
  }

  results = JSON.parse(data);
  console.log(results.count);
});

// iterate through keys in results and print them out one at a time.

Whenever I run this code, the last console.log line prints 'undefined'. For that reason, I haven't even tried iterating through the keys yet. However, I know I'm loading the .json file properly because when I do the following, I see the expected results:

results = JSON.parse(data, function(k, v) {
  console.log(k + ' : ' + v);
});

That's why I suspect it has something to do with the async nature of node. However, I'm not sure how to get around this.

Thank you for your help.

Answer 1

Your JSON is not an object with a count property.

---

results = JSON.parse(data, function(k, v) {
  console.log(k + ' : ' + v);
});

prints stuff because the callback is a "reviver", and receives each key and value.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse

If you do

results = JSON.parse(data);
for(var k in results) {
    console.log(k + ' : ' + results[k]);
}

you will see the same thing.

Answer 2

Just to point out the obvious what you are probably trying to do with results.count should instead be:

Object.keys(results).length;

But that won't give you the length including child properties only the direct keys.