Functions & Generics

Question 1

What is a function signature in TypeScript?

Answer 1

A function signature defines the parameter types and return type of a function.

Question 2

How do you define a function signature in TypeScript?

Answer 2

You specify parameter types and return type: (x: number, y: number) => number.

Question 3

What is the benefit of function signatures?

Answer 3

They improve type safety, code readability, and IDE support.

Question 4

What are optional parameters in TypeScript?

Answer 4

Parameters that may be omitted when calling a function, marked with a ?.

Question 5

What are default parameters in TypeScript?

Answer 5

Parameters that assume a default value if not explicitly passed.

Question 6

What is a rest parameter in TypeScript?

Answer 6

It collects all remaining arguments into an array using the ... syntax.

Question 7

Can rest parameters and optional parameters be used together?

Answer 7

Yes, but rest parameters must come last in the parameter list.

Question 8

What is a generic function in TypeScript?

Answer 8

A function that works with different types using a placeholder like <T>.</T>

Question 9

What is a constraint on generics in TypeScript?

Answer 9

It restricts the allowed types that a generic can accept using extends.

Question 10

Why use generics in functions?

Answer 10

To write reusable, type-safe functions that work across multiple types.

Question 11

What’s an example of a generic function?

Answer 11

function identity<T>(arg: T): T { return arg; }</T>

Question 12

How do you constrain a generic to accept only objects with a specific property?

Answer 12

Use T extends { length: number } to require a length property.

Question 13

What are advantages of optional parameters?

Answer 13

Improve flexibility and make function calls simpler when not all data is available.

Question 14

What are disadvantages of optional parameters?

Answer 14

May lead to ambiguous function behavior if overused.

Question 15

What are advantages of default parameters?

Answer 15

Avoids undefined values and provides fallback behavior without checking manually.

Question 16

What are potential issues with rest parameters?

Answer 16

They can lead to unexpected results if argument order is misunderstood.

Question 17

What’s a use case for rest parameters?

Answer 17

Variadic functions like sum(...args: number[]) or logging utilities.

Question 18

What’s a use case for generic functions?

Answer 18

Functions like map, filter, or utility methods that should work with any type.

Question 19

What’s a use case for generic constraints?

Answer 19

Validating properties in objects, like ensuring the presence of an ID or key.

Question 20

What is the impact of generics on system design?

Answer 20

They allow for highly abstract and reusable code components, reducing duplication.

Question 21

What is the architectural implication of generic functions?

Answer 21

Encourages writing DRY utility functions and shared logic modules.

Question 22

What is a performance implication of using generics?

Answer 22

None at runtime—generics are erased during compilation and don’t affect performance.

Question 23

How do generics affect debugging?

Answer 23

They provide better type safety at compile time, but don’t exist in runtime logs or stack traces.

Question 24

What’s a tradeoff of overusing generics?

Answer 24

Too much abstraction can hurt readability and make the function harder to understand.

Question 25

What’s a common interview question about generics?

Answer 25

How do you create a generic function in TypeScript and what are the benefits?

Question 26

What’s a gotcha with function overloads and generics?

Answer 26

You must ensure all overloads are compatible with the generic implementation.

Question 27

Can you combine default parameters and generics?

Answer 27

Yes, generics and default parameters can be used together to provide type and value flexibility.

Question 28

What’s a good practice for function signatures in shared interfaces?

Answer 28

Declare function types in interfaces for consistency across implementations.

Question 29

What’s a best practice for naming generic types?

Answer 29

Use clear names like T, U, V or meaningful ones like TItem or TResult for better clarity.

Question 30

What is an anti-pattern with optional parameters?

Answer 30

Using too many optional parameters instead of passing a config object can reduce maintainability.

Question 31

What is a gotcha with rest parameters and spread?

Answer 31

Using spread incorrectly can cause unexpected results or pass the wrong number of arguments.

Question 32

What’s the effect of optional parameters on TypeScript’s overload resolution?

Answer 32

They can make overloads harder to resolve if types become ambiguous.

Question 33

How does TypeScript treat unspecified optional parameters?

Answer 33

They are treated as `undefined` if not provided.

Question 34

What is a tip for debugging functions with generics?

Answer 34

Check inferred types with IDE tools or manually annotate generic parameters for clarity.

Question 35

What is a risk of not constraining generics?

Answer 35

Leads to overly permissive logic and runtime errors due to unchecked assumptions.

Question 36

Why are constraints on generics useful in libraries?

Answer 36

They allow developers to build flexible yet safe APIs with guardrails.

Question 37

What’s a performance benefit of TypeScript's generic erasure model?

Answer 37

No runtime overhead for generics—compilation strips them, improving performance.

Question 38

How do default parameters help with backward compatibility?

Answer 38

They allow new parameters without breaking existing function calls.

Question 39

What’s a common interview question about rest parameters?

Answer 39

What are rest parameters and how do they differ from arguments objects?

Question 40

What is a tuple-type rest parameter?

Answer 40

You can specify fixed types for rest parameters like `(...args: [string, number])`.

Question 41

What’s the syntax for function with default and optional params?

Answer 41

function greet(name = 'Guest', age?: number) {}

Question 42

What’s a best practice for combining function overloads and generics?

Answer 42

Use overload signatures for external type safety and a generic implementation signature internally.

Question 43

What is an anti-pattern with generic functions?

Answer 43

Making them too abstract without clear benefits, reducing readability.

Question 44

What’s the benefit of using function signatures in interfaces?

Answer 44

Provides a clear contract and improves testability of function dependencies.

Question 45

How do optional/default parameters impact unit testing?

Answer 45

They allow testing fewer cases when defaults cover common scenarios.

Question 46

What’s a debugging tip for generic constraints?

Answer 46

Temporarily replace the generic with a concrete type to isolate errors.

Question 47

Can you use multiple generic types in a function?

Answer 47

Yes, use syntax like to define multiple type parameters.