TypeScript Enum vs Union Type

Do you want to know if to use a Typescript enum or union type? In this tutorial, I will explain everything about Typescript enum vs union type. We will see enum vs. union in Typescript with examples, use cases, and differences.

In TypeScript, Enums are best used for defining a set of named constants (like directions or days of the week), providing an organized way to group related values. Union Types, on the other hand, allow a variable to hold one of several types (like a string or a number), offering more flexibility in your code. Choose Enums for a fixed set of related values and Union Types for variables that may have multiple valid types.

Table of Contents

What is TypeScript Enum?

Enums, short for enumerations, are a feature in TypeScript that allows us to define a set of named constants. This type can be numeric or string-based, offering a way to group related values under a single umbrella, making code more readable and maintainable.

Example of TypeScript Enum

enum Direction {
    Up = 1,
    Down,
    Left,
    Right
}

// Usage
let go: Direction = Direction.Up;

In this example, Direction is an enum with four values. Enums start numbering their members starting at 0. Here, Up is initialized with 1, so Down will be 2, and so on.

What is TypeScript Union Type?

Union Types in TypeScript are a way to declare a variable that could be one of several types. It’s a powerful feature that allows greater flexibility in your functions and variables.

Example of TypeScript Union Type

type StringOrNumber = string | number;

// Usage
let data: StringOrNumber;
data = "Hello"; // valid
data = 123;     // valid

In this example, StringOrNumber is a Union Type that can be either a string or a number.

Comparing Enums and Union Types

While Enums are about defining a set of named constants, Union Types are more about combining different types in Typescript. Enums offer better code organization for a group of related constants, whereas Union Types offer more flexibility in variable assignment.

Use Cases

Enum Use Case: Ideal for a set of distinct values that are closely related, like directions, days of the week, or specific states in a process.
Union Type Use Case: Best suited for variables that can legitimately hold more than one type of value, like a function that can accept both strings and numbers.

Examples

Enum Example

enum Direction {
    Up = 1,
    Down,
    Left,
    Right
}

In this example, Direction is an enum representing four directions. Enums in TypeScript can have numeric values, and here Up is explicitly set to 1. The other enum members (Down, Left, Right) are auto-incremented from Up, getting values 2, 3, and 4 respectively. This enum is useful for scenarios where you need to represent a fixed set of options, like directions in a navigation system.

Union Type Example

type StringOrNumber = string | number;

Here, StringOrNumber is a Union Type that can hold either a string or a number. This is useful in functions or variables where you might want to accept multiple types. For instance, a function could accept a numeric ID or a string username as an argument, both represented by StringOrNumber.

Here is another example:

type ID = string | number;
let userId: ID;
userId = "user123"; // valid
userId = 123;       // valid

enum vs union in Typescript

Feature	Enum	Union Type
Definition	A set of named constants	A type that can be one of several types
Use Case	Grouping related constants	Variables that can hold multiple types
Initialization	Numeric or string-based values	No initialization, just a type definition
Flexibility	Less flexible, fixed set of values	More flexible, can combine different types
Example	`enum Colors {Red, Green, Blue}`	`type StringOrNumber = string \| number;`

Conclusion

In TypeScript, both Enums and Union Types have their unique place. Enums are excellent for defining a set of related constants, bringing clarity and structure to your code. On the other hand, Union Types offer the flexibility to handle multiple data types, making your functions and variables more versatile. Understanding when to use each will significantly enhance your TypeScript coding proficiency. I hope you got an idea of “Typescript enum vs union type“.