ReadableBase.prototype.reduce - node__stream.d.ts - Node

method ReadableBase.prototype.reduce

Usage in Deno

```typescript import { ReadableBase } from "node:node__stream.d.ts"; ```



ReadableBase.prototype.reduce<T = any>(fn: (previous: any,
data: any,
options?: Pick<ArrayOptions, "signal">,
) => T,
initial?: undefined,
options?: Pick<ArrayOptions, "signal">,
): Promise<T>

This method calls *fn* on each chunk of the stream in order, passing it the result from the calculation on the previous element. It returns a promise for the final value of the reduction. If no *initial* value is supplied the first chunk of the stream is used as the initial value. If the stream is empty, the promise is rejected with a `TypeError` with the `ERR_INVALID_ARGS` code property. The reducer function iterates the stream element-by-element which means that there is no *concurrency* parameter or parallelism. To perform a reduce concurrently, you can extract the async function to `readable.map` method.

Type Parameters



T = any

Parameters



fn: (previous: any,
data: any,
options?: Pick<ArrayOptions, "signal">,
) => T

a reducer function to call over every chunk in the stream. Async or not.

optional



initial: undefined

the initial value to use in the reduction.

optional



options: Pick<ArrayOptions, "signal">

Return Type

Promise<T>

a promise for the final value of the reduction.



ReadableBase.prototype.reduce<T = any>(fn: (previous: T,
data: any,
options?: Pick<ArrayOptions, "signal">,
) => T,
initial: T,
options?: Pick<ArrayOptions, "signal">,
): Promise<T>

Type Parameters



T = any

Parameters



fn: (previous: T,
data: any,
options?: Pick<ArrayOptions, "signal">,
) => T



initial: T

optional



options: Pick<ArrayOptions, "signal">

Return Type

Promise<T>