Programmatically running JavaScript with Node.js

Question

I need to programmatically (in Java) run JavaScript with Node.js and read the error. There are two approach:

1. call node -e <javascript>
2. Save the JavaScript to a temp file, and call node temp.js

How are they different?

It seems that the first approach is more efficient, but when I run something like

process.on('uncaughtException', function(err) {
    console.error(typeof(err));
});
function x_5(x_6, x_7) {
  var x_8 = Infinity;
}
throw x_5;

It prints

[eval]:8
throw x_5;
      ^
function

But all I wanted was just the last line. The second approach only gave me the last line. So I am trying to understand how the two approaches are different, and how I can get rid of the unnecessary error message.

Answer 1

as you see node -e script will dump exception to stderr, so you can print the result to stdout.

console.log instead of console.error

process.on('uncaughtException', function(err) {
    console.log(typeof(err));
});

on java side, take result from stdout, ignore stderr

String[] command = {"node", "-e", js};
Process p = Runtime.getRuntime().exec(command);
InputStream in = p.getInputStream();
for (int i = 0; i < in.available(); i++) {
    System.out.println("" + in.read());
}