An interface defines a contract; a class can implement many interfaces and interfaces can have default/static methods but no instance state. An abstract class can hold fields, constructors and partial implementation, but a class can extend only one. Use interfaces for capabilities and abstract classes for shared base behavior.
Advanced answer
Deep dive
Expanding on the short answer — what usually matters in practice:
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.
Examples
A tiny example (an explanation template):
// Example: discuss trade-offs for "interface-vs-abstract-class?"
function explain() {
// Start from the core idea:
// Interfaces allow multiple implementation (contracts). Abstract classes can have state, con
}
Common pitfalls
Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).