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.
Need a nudge?
Ask about this lesson or your next move. The guide explains the path without taking the work away from you.
Ready for the next lesson?
Mark this lesson complete when you have finished the exercise.
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