Test Case that shows a high number of writes getting mangled along with a file to scan over and validate the data.

read.js

var fs = require('fs');
var lines = fs.readFileSync('output.json', 'utf8').split("\n");
lines.pop(); // remove the last (empty) new line
for(var n in lines) {
  try {
    JSON.parse(lines[n]);
  } catch (e) {
    console.log("Error at line " + (n+1) + " => " + lines[n]);
  }
}

write.js

var fs = require('fs');
var fd = fs.openSync('output.json', 'a');
var i = 0;
while (i < 100000) fs.write(fd, JSON.stringify({ foo: 'bar', iteration: i++ })+"\n");
fs.closeSync(fd);