`simulateReadableStream()`

simulateReadableStream is a utility function that creates a ReadableStream which emits provided values sequentially with configurable delays. This is particularly useful for testing streaming functionality or simulating time-delayed data streams.

import { simulateReadableStream } from 'ai';

const stream = simulateReadableStream({
  chunks: ['Hello', ' ', 'World'],
  initialDelayInMs: 100,
  chunkDelayInMs: 50,
});

Import

import { simulateReadableStream } from "ai"

API Signature

Parameters

chunks:

T[]

Array of values to be emitted by the stream

initialDelayInMs?:

number | null

Initial delay in milliseconds before emitting the first value. Defaults to 0. Set to null to skip the initial delay entirely.

chunkDelayInMs?:

number | null

Delay in milliseconds between emitting each value. Defaults to 0. Set to null to skip delays between chunks.

Returns

Returns a ReadableStream<T> that:

Emits each value from the provided chunks array sequentially
Waits for initialDelayInMs before emitting the first value (if not null)
Waits for chunkDelayInMs between emitting subsequent values (if not null)
Closes automatically after all chunks have been emitted

Type Parameters

T: The type of values contained in the chunks array and emitted by the stream

Examples

Basic Usage

const stream = simulateReadableStream({
  chunks: ['Hello', ' ', 'World'],
});

With Delays

const stream = simulateReadableStream({
  chunks: ['Hello', ' ', 'World'],
  initialDelayInMs: 1000, // Wait 1 second before first chunk
  chunkDelayInMs: 500, // Wait 0.5 seconds between chunks
});

Without Delays

const stream = simulateReadableStream({
  chunks: ['Hello', ' ', 'World'],
  initialDelayInMs: null, // No initial delay
  chunkDelayInMs: null, // No delay between chunks
});