Advanced Types
Indexed Access Types
Master Indexed Access Types (T[K]) in TypeScript, extracting nested property types, array element types, and union key lookups.
Last Updated: July 29, 2026
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10 min read
An Indexed Access Type (also known as a Lookup Type) allows you to look up the exact type of a specific property on another type using bracket notation Type[Key].
1. Syntax for Indexed Access Types
Basic Property Extraction
2. Union Indexing (keyof)
Indexing with a union of keys extracts a union of the corresponding property types:
3. Extracting Array Element Types (T[number])
You can extract the element type of an array or tuple by indexing with the number keyword or a numeric index:
4. Interactive Code Playground
Test indexed access types below:
5. Summary Table
| Lookup Expression | Target Type | Result |
|---|---|---|
Type["prop"] | Object Type | Type of property "prop" |
Type[keyof Type] | Object Type | Union of all property value types |
ArrayType[number] | Array Type T[] | Element type T |
TupleType[0] | Tuple [A, B] | First element type A |