typescript enum vs type: practical differences and use cases

choosing between enums and types in typescript impacts your code’s maintainability and type safety. let’s explore when to use each.

problem: enum or type?

developers often debate whether to use an enum or a type when defining a set of related constants. while both serve similar purposes, they have distinct characteristics that affect their usage in different scenarios.

solution: comparing enums and types

to make an informed decision, let’s examine the pros and cons of each approach and explore how they interact with other typescript features, particularly interfaces.

enums: named constants with runtime presence

enums in typescript provide a way to define named constants with runtime representation.

enum TimeTravel {
  Past = 'past',
  Present = 'present',
  Future = 'future'
}

console.log(TimeTravel.Future); // Output: 'future'

pros:

• define a set of named constants
• can have numeric or string values
• typescript can infer types from enums

cons:

• generate additional javascript at runtime
• can be mutated (though this is rarely desirable)
• limited to number or string values

types: lightweight and flexible

types offer a more flexible and lightweight alternative.

type TimeTravelDestination = 'past' | 'present' | 'future';

const destination: TimeTravelDestination = 'future';
console.log(destination); // Output: 'future'

pros:

• no runtime overhead
• can represent more complex types (unions, intersections, etc.)
• immutable by design

cons:

• don’t create a named object (no reverse mapping)
• can’t be used in some places where enums can (e.g., certain decorators)

key implementation details

when working with interfaces, enums can provide a powerful combination:

enum FuelType {
  Plutonium = 'plutonium',
  MrFusion = 'mr_fusion'
}

interface TimeMachine {
  model: string;
  fuelType: FuelType;
  destination: TimeTravel;
}

const delorean: TimeMachine = {
  model: 'DMC-12',
  fuelType: FuelType.MrFusion,
  destination: TimeTravel.Future
};

this approach provides type safety and self-documentation, making your code more robust and readable.

potential pitfalls

1. runtime implications: enums generate javascript objects, which can increase bundle size.
2. type inference: typescript might infer a more specific type than you intend with enums.
3. const assertions: with types, you might need to use as const to get similar behavior to enums in some cases.

conclusion: choosing the right tool

choosing between enums and types depends on your specific use case:

• use enums when you need a named set of constants with runtime objects
• prefer types for lightweight, compile-time-only type checking

both have their place in your typescript toolkit. the key is knowing when to use each to ensure your code remains maintainable and type-safe.