What this snippet does
Type aliases strictly enforce their definitions, rejecting types not explicitly included in a union.
Expected output
Compile Error: Type 'boolean' is not assignable to type 'string | number'.
Why practise typing this
Typing type aliases vs interfaces code builds muscle memory for the symbols and indentation TypeScript uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.
More TypeScript practice
- Creating a simple type aliasType Aliases vs Interfaces · beginner
- Defining an object shape with a type aliasType Aliases vs Interfaces · beginner
- Comparing type and interface syntaxType Aliases vs Interfaces · beginner
- Using a type alias for a recursive JSON structureType Aliases vs Interfaces · beginner
- Attempting to declare a duplicate type aliasType Aliases vs Interfaces · beginner
- Defining a constructable type aliasType Aliases vs Interfaces · advanced