What are the best practices for securing JavaScript applications against XSS and Prototype Pollution?

All answers to this question.

To prevent Prototype Pollution, use Object.create(null) for objects that store user-controlled keys, which ensures they don't inherit from Object.prototype. Always use a library like DOMPurify for sanitizing HTML before rendering it to prevent XSS. On the backend, implement strict JSON schema validation to ensure incoming objects don't contain forbidden keys like __proto__. Additionally, setting a strong Content Security Policy (CSP) header is your best defense-in-depth against XSS, as it can block unauthorized scripts from executing even if an injection occurs.

   Answered 2025-07-22 by Patricia Roberts

Are you currently using any automated security scanning tools like Snyk or npm audit in your CI/CD pipeline to catch vulnerable dependencies before they reach production?

   Answered 2025-08-10 by Daniel Martinez

• We use npm audit, but it doesn't always catch logical flaws like prototype pollution in our custom code. I'm looking for a more manual code-review checklist. We are planning to implement a "No-Dynamic-Keys" policy for object assignments, which should theoretically stop most of these attacks at the source. Do you think that is too restrictive for a large dev team?

     Commented 2025-08-20 by Brian Fletcher

Using Object.freeze() on your prototypes at the start of your application execution can act as a final "fail-safe" against most basic pollution attempts.

   Answered 2025-09-05 by Melissa Young

• I agree with Melissa. Freezing the prototype is a bold but effective move for high-security environments where you really can't risk any runtime modifications.

     Commented 2025-09-12 by Kevin Adams