Description

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Beginner · 10 min

Optional and nullable values

Check missing values instead of assuming that they exist.

Read an optional property

A question mark marks an optional property. Reading it may produce undefined. Optional chaining skips the access when the value is missing.

type User = { name: string; nickname?: string };
const user: User = { name: "Ada" };
console.log(user.nickname?.toUpperCase() ?? user.name);

Output

Ada

Handle null explicitly

With strictNullChecks, null is not automatically allowed wherever a string is expected. Include it in the type when it is a real possibility, then handle it.

function displayName(name: string | null): string {
  return name ?? "Guest";
}
console.log(displayName(null));

Output

Guest

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

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Handle a missing nickname

Display "Guest" when "nickname" is absent. Otherwise display the uppercase nickname.

Practice