JS read json file and use as an object

Question

I'm trying so get the number of items in the array inside this piece

JSON

{
  "collection" : [
    {
      "item": "apple"
    },
    {
      "item": "banana"
    }]
}

Using the following JS (NodeJS): Updated with answers from user 'elssar'

var data = JSON.parse(fs.readFileSync(filePath));
console.log(data.collection.length);

Expected result: 2

Without specifying the encoding data will be a buffer instead of string (thanks to user nils). JSON.parse should work for both. Now I'm getting an error Unexpected token ? at Object.parse (native). Any idea how to fix this? (using Node 5.2.0)

Possible duplicate of Why does Node.js' fs.readFile() return a buffer instead of string? — nils
– nils, Commented Jan 14, 2016 at 12:14
@nils not really a duplicate, as setting the content type would only give the op a string, which does not solve his problem — elssar
– elssar, Commented Jan 14, 2016 at 12:17

elssar · Accepted Answer · 2016-01-14 12:44:51Z

27

You need to parse the content of the file to JSON.

fs.readFile(filePath, function (error, content) {
    var data = JSON.parse(content);
    console.log(data.collection.length);
});

Or

var data = JSON.parse(fs.readFileSync(filePath));

Alternatively, you could just require json files (the file extension needs to be .json)

var data = require(filePath);
console.log(data.collection.length);

edited Jan 14, 2016 at 12:44

answered Jan 14, 2016 at 12:16

elssar

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14 Comments

nils Over a year ago

Your first snippet will probably not work, as data is undefined, and even if you used content, it would be a buffer.

elssar Over a year ago

@nils oops. fixed :)

Matthijs van Hest Over a year ago

Spotted that as well. Still it doesn't work for me. It still says that data is undefined. The alternative you gave me seems to work. But why is my Intelli saying it IS an built-in function but also states: use of an implicitly declared global variable 'require' ??

nils Over a year ago

You still haven't set an encoding... look at my duplicate link.

elssar Over a year ago

@nils not required. JSON.parse works without setting the encoding

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