codex-lv4-may-2025

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Level 21: Enforce Basic Validation

• Ensure required fields are present and short-circuit with 400 plus an error message when data is missing.
• Add default values or type checks as needed to keep the data structure consistent.
• Reminder: Validate fields appropriate for your resource type, not just the example items fields.

Show Me: validation check

if (!req.body?.title) {
  return res.status(400).json({ error: 'Title is required' });
}

Understanding the shorthand: !req.body?.title uses two JavaScript features:

• Optional chaining (?.): Safely accesses title even if req.body is undefined or null. Without ?, accessing req.body.title when req.body is undefined would throw an error.
• Logical NOT (!): Negates the value, so the condition is true when title is missing, empty string, null, undefined, 0, or false.

This is equivalent to: if (!req.body || !req.body.title) but more concise and safer.