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
• defer() — create or acquire a source only when its graph is activated
• fromEvent() — adapt hot EventTarget and EventEmitter sources
• pipeline() — define a reusable typed operator chain
• destination() — define a reusable terminal consumer with setup and cleanup
• 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() — retain the first value for each identity, selected key, or field tuple
• slice(), take(), drop(), head(), and last() — select by position
• stopWhen() — include the first match and stop the branch

Aggregate and order

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

Async work

• mapAsync() — transform with concurrency, ordering, retry, local recovery, timeout, and cancellation controls
• makeAsync() — yield long synchronous pipelines to the event loop

Flow control

• throttle() — drop values inside a time window
• rateLimit() — delay values to enforce a local burst 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 concurrency
• through() — attach a pipeline, 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() — decode and tokenize lines or custom regular-expression-delimited text across chunk boundaries
• encode() and decode() — transform streaming base64

Consume

• pipeTo() — run an Exstream destination or write to a Node or Web writable
• for await...of — consume one value at a time
• toArray(), single(), and drain() — finish with uniform promise semantics

Interop

• toWebReadable() and toNodeReadable() — expose platform readables from a source-backed Exstream
• toNodeTransform() — expose a reusable pipeline as a native Node transform

Low-level API

• write() and end() — implement manual sources
• consume() and consumeSync() — build custom operators
• start() — freeze and activate an explicitly gated source graph