Errors and Exit Codes

Part of the Node.js Basics section of Coddy's Node.js journey. Lesson 4 of 24.

When a command fails, the terminal and the scripts that call your program need to know.

A program has two output streams: stdout for results and stderr for errors, written with console.error. When it ends it hands back an exit code: 0 means it worked, anything else means it failed. process.exit(1) stops the program at once with code 1.

// node divide.js 6 0
const [a, b] = process.argv.slice(2).map(Number);
if (b === 0) {
    console.error('Cannot divide by zero');
    process.exit(1);
}
console.log(a / b);

The terminal beside your code shows stderr in red and prints the exit code when it is not 0.

Challenge

Easy

With no command, print Usage: node notes.js <command> [words] to stderr and exit with code 1.
An unknown command prints Unknown command: <word> and then the usage line, both to stderr, and exits with 1.

Run node notes.js, then node notes.js remove 3.

Try it yourself

// Your notes tool starts here.
const [command, ...words] = process.argv.slice(2);
const text = words.join(' ');

if (command === 'add') {
    console.log(`Adding: ${text}`);
} else if (command === 'list') {
    console.log('No notes yet');
} else {
    console.log(`Unknown command: ${command}`);
}