Lesson 38 of 55
15 mins readThe typeof Type Operator
In Plain English
TypeScript adds a typeof operator you can use in a type context to refer to the type of an existing variable, function, or object value without duplicate interface definitions.
Core Rules to Remember
Type Context typeof: Derives types directly from runtime constants and configuration objects.
DRY Principle: Eliminates redundant interface definitions for static constants.
Live Interactive Example
Hit Run Code to see it liveDeriving Types from Runtime Constants
Python 3.12
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Output Console
Click "Run Code" to view the rendered output.
How it works: AppTheme captures the exact nested structure of defaultTheme.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Derive Action Type from Object
- Define const sampleAction = { type: "FETCH_USER", payload: { id: 101 } } as const.
- Derive type ActionType = typeof sampleAction.
- Create const act: ActionType = sampleAction and print act.type.
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Sandbox Output
Click "Run & Check" to test your solution.
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