API reference

Operator index

Find the complete public API by intent. Every page covers signatures, accepted values and defaults, execution, pressure, memory, context, errors, cancellation, runtimes, forms, and edge cases that change real behavior.

Create

• exstream() — adapt iterables, promises, platform streams, generators, or a writable source
• fromEvent() — adapt hot EventTarget and EventEmitter sources
• pipeline() — define a reusable typed operator chain
• data() and nil — distinguish data from error and end control records

Context

• withContext() and extendContext() — attach synchronous or asynchronous record metadata
• Stream state — inspect lifecycle, buffering, drops, pressure, and cancellation
• Events — observe errors, aborts, completion, fatal failures, and drain

Transform

• map(), flatMap(), and flatten() — reshape or expand values
• tap() and compact() — add synchronous effects or remove falsy values
• pluck(), pick(), and omit() — reshape object records
• batch() — group records into bounded arrays

Select

• filter() and reject() — keep or drop by synchronous predicate
• find(), where(), and findWhere() — find by predicate or shallow object match
• uniq() and uniqBy() — retain the first value for each identity or key
• slice(), take(), drop(), head(), and last() — select by position
• stopWhen() — include the first match and stop the branch

Aggregate and order

• collect(), reduce(), and reduce1() — produce one result after completion
• groupBy() and keyBy() — build a complete grouped or unique-key index
• sort() and sortBy() — order a complete finite stream
• sortedGroupBy() — group adjacent equal keys without retaining the whole stream

Async work

• mapAsync() — transform with concurrency, ordering, retry, timeout, and cancellation controls
• asyncFilter() and asyncReduce() — await sequential selection or aggregation
• resolve(), massThen(), and massCatch() — work with streams of promises
• makeAsync() — yield long synchronous pipelines to the event loop

Flow control

• throttle() — drop values inside a time window
• ratelimit() — delay values to enforce a maximum rate

Branch and combine

• fork() — create a reliable branch participating in backpressure
• observe() — create a non-blocking, explicitly buffered observer
• merge() — consume a stream of streams with bounded parallelism
• through() — attach a pipeline, stream, function, or Node transform
• sortedJoin() — merge-join exactly two pre-sorted streams

Errors

• Error API — inspect record metadata, provenance, format errors, overflow, and timeouts
• errors() and skipErrors() — recover, replace, or drop record errors
• failOnError() and stopOnError() — promote or stop at the first record error
• routeErrors() — split data and dead letters into reliable branches

Formats

• csv() and csvStringify() — incremental CSV parsing and serialization
• json() and jsonStringify() — stream one JSON document or array envelope
• jsonl() and jsonlStringify() — parse and serialize line-delimited JSON
• split() and splitBy() — decode and tokenize text across chunk boundaries
• encode() and decode() — transform streaming base64

Consume

• pipe() and pipeTo() — connect a destination with native or promise completion semantics
• toAsyncIterator() — consume one value per for await demand
• toWebReadable() and toNodeStream() — expose platform streams
• toArray(), toPromise(), and drain() — finish through callbacks or promises
• value(), values(), and valuesSync() — collect with cardinality or synchrony checks

Low-level API

• write(), writeData(), and pull() — implement manual sources and demand
• consume(), consumeSync(), and each() — build custom operators or callback terminals
• start(), pause(), and resume() — control source gates and adapters
• end(), destroy(), abort(), and fail() — choose the correct terminal transition
• extend() and Utilities — extend the prototype or reuse exported helpers