Using exec throws process error after save in node webkit - node.js

Question

I'm using exec() in node webkit to open a file in the operating system's default program using start filename after it saves the file. Here is my code:
var fs = require('fs');
var myFile = "C:/TEMP/" + fileName;
fs.writeFile(myFile, rtf, function(err) {
if(err) {
alert("error");
}
});
var sys = require('sys');
var exec = require('child_process').exec;
var child;
child = exec("start " + myFile, function (error, stdout, stderr) {
if (error !== null) {
console.log('exec error: ' + error);
}
});
Sometimes it works, but sometimes I'm getting this error: exec error: Error: Command failed: The process cannot access the file because it is being used by another process.
Edit: I saw that Microsoft has this issue with rtf and txt documents opening in wordpad (which is what mine was being opened in), so I thought it might have been that process hanging up and not dying properly. Before I called it quits for the night, I changed the default program to open in Libre Office and had better results (it didn't happen as often), but if I tried to fire the function quickly in sequence, I would still get the error.

Answer 1

writeFile is async. You need a callback like this:
var fs = require('fs');
var myFile = "C:/TEMP/" + fileName;
fs.writeFile(myFile, rtf, function(err) {
if(err) {
alert("error");
}else{
lire();
});
var sys = require('sys');
var exec = require('child_process').exec;
var child;
function lire(){
child = exec("start " + myFile, function (error, stdout, stderr) {
if (error !== null) {
console.log('exec error: ' + error);
}
});
};