Description

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Beginner · 10 min

Literal unions

Limit a value to a small set of meaningful choices.

Describe allowed choices

A literal union lists exact allowed values. It catches a misspelled choice in your code. It does not automatically check strings received from outside the program.

type Status = "draft" | "sent";
const status: Status = "sent";
console.log(status);

Output

sent

Branch on a known choice

A function can accept a literal union instead of any string. The type describes its callers while the function still uses ordinary JavaScript conditions.

type Size = "small" | "large";
function price(size: Size): number { return size === "large" ? 8 : 5; }
console.log(price("small"));

Output

5

Put it into practice

  1. Read the types and predict the output before running the examples.
  2. Complete the task, then check your understanding with the practice questions.

Try it yourself

Code runs on this device. When you are signed in, drafts sync to your account.

Choose a valid status

Assign the allowed value "sent" to "status" and display it. Keep the literal union.

Practice