Catching Fatal Errors with Node.js child_process
I'm relatively new to hardcore Node.js hacking so I'm seeing all sorts of lovely new errors that I have no clue how to solve when I initially see them. To this point I've managed to keep a smile on my face while trying to fix these errors, a quality I quite enjoy about myself. One of the recent errors I encountered was with child_process, whereby an error would occur within an execSync command and the entire app would brick; not even a try/catch would save me. I did find a solution, however.
The JavaScript
The best way to catch errors without letting your app brick is by using the process' spawn (or in this case spawnSync) method:
var childProcess = require('child_process');
var commitMessage = (function() {
var spawn = childProcess.spawnSync('git', ['log', '--format=%B', '-n', '1']);
var errorText = spawn.stderr.toString().trim();
if (errorText) {
console.log('Fatal error from `git log`. You must have one commit before deploying.');
throw new Error(errorText);
}
else {
return spawn.stdout.toString().trim();
}
})();
With this method you can check the stderr buffer first; if there's a String from it you know it errored out, if no error text then the process was clean!
there is also a
spawn.statusproperty that holds the exit code. A check forspawn.status !== 0might be more reliable in cases when there no error message…also,
spawn.stderr.toString()is not safe, asstderrmay be undefined.you’re better off just wrapping it with the
Stringconstructor:Perhaps it is more elegant to use status to judge whether the execution was successful or not.
const childProcess = require('child_process'); var result = (() => { const { stderr, stdout, status } = childProcess.spawnSync('npm', ['install']); if (status !== 0) { const errorText = stderr.toString(); console.log('Fatal error fromnpm install.'); throw new Error(errorText); } return stdout.toString(); })();