TypeScript in Depth · Type Basics · Lesson 3 of 16
Union and Literal Types
Concept
Union and Literal Types
Union types let a value be one of several types. Literal types restrict it to specific exact values.
By the end of this lesson
- Explain the core idea behind Union and Literal Types.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
How to study this page
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Union and Literal Types. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Declare a variable typed as either a number or a string, and assign both in turn.
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