sarahbkim sarahbkim - 3 months ago 7
Javascript Question

Write objects into file with Node.js

I've searched all over stackoverflow / google for this, but can't seem to figure it out.

I'm scraping social media links of a given URL page, and the function returns an object with a list of URLs.

When I try to write this data into a different file, it outputs to the file as

[object Object]
instead of the expected:
[ 'https://twitter.com/#!/101Cookbooks',
'http://www.facebook.com/101cookbooks']
as it does when I
console.log()
the results.

This is my sad attempt to read and write a file in Node, trying to read each line(the url) and input through a function call
request(line, gotHTML)
:

fs.readFileSync('./urls.txt').toString().split('\n').forEach(function (line){
console.log(line);
var obj = request(line, gotHTML);
console.log(obj);
fs.writeFileSync('./data.json', obj , 'utf-8');
});


for reference -- the
gotHTML
function:

function gotHTML(err, resp, html){
var social_ids = [];

if(err){
return console.log(err);
} else if (resp.statusCode === 200) {
var parsedHTML = $.load(html);


parsedHTML('a').map(function(i, link){
var href = $(link).attr('href');
for(var i=0; i<socialurls.length; i++){
if(socialurls[i].test(href) && social_ids.indexOf(href) < 0 ) {
social_ids.push(href);
};
};
})
};

return social_ids;

};

Answer

obj is an array in your example.

fs.writeFileSync(filename, data, [options]) requires either String or Buffer in the data parameter. see docs.

Try to write the array in a string format:

// writes 'https://twitter.com/#!/101Cookbooks', 'http://www.facebook.com/101cookbooks'
fs.writeFileSync('./data.json', obj.join(',') , 'utf-8'); 

Or:

// writes ['https://twitter.com/#!/101Cookbooks', 'http://www.facebook.com/101cookbooks']
var util = require('util');
fs.writeFileSync('./data.json', util.inspect(obj) , 'utf-8');

edit: The reason you see the array in your example is because node's implementation of console.log doesn't just call toString, it calls util.format see console.js source