Literal types

Learn literal types, fixed value types.

What is a literal type?

A literal type is a type that specifies an exact value. Combined with unions, you create precise types that allow only specific values.

let direction: "up" | "down";
direction = "up";
direction = "left";  // error

This is useful when a variable can take only a few fixed values.

Literal unions

You can combine several literal types with | to create a finite set of values. This is similar to a string enum but offers a simpler alternative.

type Status = "open" | "closed" | "pending";
function setStatus(s: Status) {
  // ...
}
setStatus("open");
setStatus("done");  // error

Type safety is provided at compile time.

Exercise Define a role with a literal union

Define the Role type as "admin" | "user" | "guest". Write a function greet(role: Role): string that returns "Welcome, admin" for admin, "Hello, user" for user, and "Hi, guest" for guest. Print the result of all three calls.

Show example solution

type Role = "admin" | "user" | "guest";

function greet(role: Role): string {
  if (role === "admin") {
    return "Welcome, admin";
  } else if (role === "user") {
    return "Hello, user";
  } else {
    return "Hi, guest";
  }
}

console.log(greet("admin"));
console.log(greet("user"));
console.log(greet("guest"));

Test yourself

Which of the following is an example of a literal type?
```
let direction: ??? = "left";
```
- string | number
- "left" | "right"
- Object
- string
Show answer

"left" | "right" — A literal type uses an exact value (such as "left" or 42) as the type. "left" | "right" is a union of two string literals.

Complete the literal value

let color: "red" | "blue" = ____;

Show answer

let color: "red" | "blue" = "red";

Literal parts

"up"

A single string literal
42

A single number literal
"left" | "right"

A union of two string literals
type Status = "open" | "closed"

A type made of a literal union

Next lesson: Summary - Union & intersection

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