Implement Stack and Queue in JavaScript

Challenge summary

Implement stack and queue data structures with predictable constant-time core operations.

What you'll practice

• Preserve last-in-first-out behavior for stack operations.
• Preserve first-in-first-out behavior for queue operations.
• Handle empty reads and repeated queue removals without costly array shifts.

What Premium unlocks

Premium unlocks the runnable workspace, behavioral checks, implementation walkthrough, and edge-case discussion.