API reference / @evolu/common / Types / RefinementWithIndex

Type Alias: RefinementWithIndex()<A, B>

type RefinementWithIndex<A, B> = (a, index) => a is B;

Defined in: packages/common/src/Types.ts:82

A type guard function that refines type A to a narrower type B at a given index.

Useful for callbacks that need both the element and its position while maintaining type narrowing.

Example

type Item = { type: "number" | "string"; value: unknown };

const isNumberItem: RefinementWithIndex<Item, Item & { type: "number" }> =
  (item, index): item is Item & { type: "number" } =>
    index > 0 && item.type === "number";

const items: ReadonlyArray<Item> = [...];
const [numbers, others] = partitionArray(items, isNumberItem);

Type Parameters

Type Parameter
`A`
`B` extends `A`

Parameters

Parameter	Type
`a`	`A`
`index`	`number`

Returns

a is B