Error when trying to parse a string into JSON from .json file in node js

Question

Error when trying to parse a string into JSON from .json file in node js

var jsonObject = collages;

file.writeFile('collage.json', JSON.stringify(jsonObject), function(err){
    if (err) throw err;
    console.log('Success');
});


var result = '';
result += file.readFile('collage.json', 'utf-8', function(err, data) {
    if(err) throw err;
    console.log(data);
});
JSON.parse(result);

I'm getting an "SyntaxError: Unexpected token u - at Object.parse(native)"

I'm new to JSON and I can't seem to recreate the object that I write out. When I print out result I have the stringified json object, however when I try to parse that string the error is given. The object collages is simply an array of layer objects which hold 6 fields (x value, y value, width...etc). Any help would be much appreciated, I want to read in the JSON object so that I can recreate the collage when it is read in.

javascript
json
node.js
filesystems

Answer 1

file.readFile is an asynchronous action and you are acting like it is synchronous.

Answer 2

readFile is asynchronous, so you just need to rearrange your code a bit:

var result = null;

file.readFile('collage.json', 'utf-8', function(err, data) {
    if(err) throw err;
    result = JSON.parse(data);
});

Remember that with asynchronous functions, you have to execute dependent code in the callback.

Answer 3

You can do this synchronously using readFileSync for example:

var result = file.readFileSync('collage.json').toString();

In the case of a json file, Node.js provides an even simpler way to accomplish this:

var result = require('./callage.json');

require will notice the .json extension and parse the file as json for you.

http://nodejs.org/api/fs.html#fs_fs_readfilesync_filename_options http://nodejs.org/api/modules.html#modules_file_modules