Generics
Default Type Parameters
Master Default Type Parameters (<T = DefaultType>) in TypeScript, providing fallback generic types for functions, interfaces, and classes.
Last Updated: July 29, 2026
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10 min read
In TypeScript, Default Type Parameters allow you to specify a fallback type for a generic parameter . If a caller does not explicitly specify or provide a type that allows inference, TypeScript falls back to the default type.
1. Syntax for Default Type Parameters
Assign a default type using the = operator inside angle brackets :
2. Combining Constraints with Defaults
You can combine generic constraints (extends) with default parameters (=). The default type parameter MUST satisfy the constraint.
3. Parameter Order Rule for Defaults
Just like function default parameters, generic default parameters must come after all required generic type parameters without defaults.
4. Interactive Code Playground
Test default type parameters below:
5. Summary Table
| Concept | Syntax Example | Meaning |
|---|---|---|
| Default Parameter | | T defaults to string if unspecified |
> | T must extend object and defaults to Record |