Node.JS fs.readFileSync() bad arguments

Question

I'm getting the following error in my Node and can't figure out why:

TypeError: Bad arguments
    at Object.fs.readFileSync (fs.js:277:11)
    at getSeries (/Users/user/tv/final.js:57:16)
    at /Users/user/tv/final.js:89:4
    at /Users/user/tv/node_modules/async/lib/async.js:610:21
    at /Users/user/tv/node_modules/async/lib/async.js:249:17
    at iterate (/Users/user/tv/node_modules/async/lib/async.js:149:13)
    at /Users/user/tv/node_modules/async/lib/async.js:160:25
    at /Users/user/tv/node_modules/async/lib/async.js:251:21
    at /Users/user/tv/node_modules/async/lib/async.js:615:34
    at /Users/user/tv/final.js:86:4

I'm pretty sure it has nothing to do with the async npm package I'm using as I got the same error before I started using it.

Here is the code:

    function getSeries() {
    JSON.parse(fs.readFileSync('updates.json', function(err,data) {
        if (err) {
           console.error(err);
        }
        else {
           var json = data;
        }
}));

Answer 1

You are mixing asynchronous and synchronous in a bad way. You are confusing different stuff.

Your code should be either like this (synchronous):

try {
    var json = JSON.parse(fs.readFileSync('updates.json'));
} catch (err) {
    console.error(err);
}

or asynchronous:

fs.readFile('updates.json', function(err,data) {
    if (err) {
       console.error(err);
    }
    else {
       var json = JSON.parse(data);
    }
});

The difference comes that fs.readFile (docs) expects a callback and will give you the error/result by calling the callback given. It doesn't return anything.

And fs.readFileSync (docs) doesn't accept a callback, because it's synchronous and it returns the result or throws the error.

Also if you are parsing .json statically, you can use require:

var json = require('./updates')

Note that, require function will cache it's output and on the subsequent runs it will return the same object without blocking or doing any IO.