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964 lines
24 KiB
964 lines
24 KiB
4 years ago
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# BFJ
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[](https://gitlab.com/philbooth/bfj/pipelines)
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[](https://www.npmjs.com/package/bfj)
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[](https://www.npmjs.com/package/bfj)
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[](https://opensource.org/licenses/MIT)
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Big-Friendly JSON. Asynchronous streaming functions for large JSON data sets.
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* [Why would I want those?](#why-would-i-want-those)
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* [Is it fast?](#is-it-fast)
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* [What functions does it implement?](#what-functions-does-it-implement)
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* [How do I install it?](#how-do-i-install-it)
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* [How do I read a JSON file?](#how-do-i-read-a-json-file)
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* [How do I parse a stream of JSON?](#how-do-i-parse-a-stream-of-json)
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* [How do I selectively parse individual items from a JSON stream?](#how-do-i-selectively-parse-individual-items-from-a-json-stream)
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* [How do I write a JSON file?](#how-do-i-write-a-json-file)
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* [How do I create a stream of JSON?](#how-do-i-create-a-stream-of-json)
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* [How do I create a JSON string?](#how-do-i-create-a-json-string)
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* [What other methods are there?](#what-other-methods-are-there)
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* [bfj.walk (stream, options)](#bfjwalk-stream-options)
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* [bfj.eventify (data, options)](#bfjeventify-data-options)
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* [What options can I specify?](#what-options-can-i-specify)
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* [Options for parsing functions](#options-for-parsing-functions)
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* [Options for serialisation functions](#options-for-serialisation-functions)
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* [Is it possible to pause parsing or serialisation from calling code?](#is-it-possible-to-pause-parsing-or-serialisation-from-calling-code)
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* [Can it handle newline-delimited JSON (NDJSON)?](#can-it-handle-newline-delimited-json-ndjson)
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* [Why does it default to bluebird promises?](#why-does-it-default-to-bluebird-promises)
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* [Can I specify a different promise implementation?](#can-i-specify-a-different-promise-implementation)
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* [Is there a change log?](#is-there-a-change-log)
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* [How do I set up the dev environment?](#how-do-i-set-up-the-dev-environment)
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* [What versions of Node.js does it support?](#what-versions-of-nodejs-does-it-support)
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* [What license is it released under?](#what-license-is-it-released-under)
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## Why would I want those?
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If you need
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to parse huge JSON strings
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or stringify huge JavaScript data sets,
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it monopolises the event loop
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and can lead to out-of-memory exceptions.
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BFJ implements asynchronous functions
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and uses pre-allocated fixed-length arrays
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to try and alleviate those issues.
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## Is it fast?
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No.
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BFJ yields frequently
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to avoid monopolising the event loop,
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interrupting its own execution
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to let other event handlers run.
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The frequency of those yields
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can be controlled with the [`yieldRate` option](#what-options-can-i-specify),
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but fundamentally it is not designed for speed.
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Furthermore,
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when serialising data to a stream,
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BFJ uses a fixed-length buffer
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to avoid exhausting available memory.
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Whenever that buffer is full,
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serialisation is paused
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until the receiving stream processes some more data,
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regardless of the value of `yieldRate`.
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You can control the size of the buffer
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using the [`bufferLength` option](#options-for-serialisation-functions)
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but really,
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if you need quick results,
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BFJ is not for you.
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## What functions does it implement?
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Nine functions
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are exported.
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Five are
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concerned with
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parsing, or
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turning JSON strings
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into JavaScript data:
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* [`read`](#how-do-i-read-a-json-file)
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asynchronously parses
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a JSON file from disk.
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* [`parse` and `unpipe`](#how-do-i-parse-a-stream-of-json)
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are for asynchronously parsing
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streams of JSON.
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* [`match`](#how-do-i-selectively-parse-individual-items-from-a-json-stream)
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selectively parses individual items
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from a JSON stream.
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* [`walk`](#bfjwalk-stream-options)
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asynchronously walks
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a stream,
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emitting events
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as it encounters
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JSON tokens.
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Analagous to a
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[SAX parser][sax].
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The other four functions
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handle the reverse transformations,
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serialising
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JavaScript data
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to JSON:
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* [`write`](#how-do-i-write-a-json-file)
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asynchronously serialises data
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to a JSON file on disk.
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* [`streamify`](#how-do-i-create-a-stream-of-json)
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asynchronously serialises data
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to a stream of JSON.
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* [`stringify`](#how-do-i-create-a-json-string)
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asynchronously serialises data
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to a JSON string.
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* [`eventify`](#bfjeventify-data-options)
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asynchronously traverses
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a data structure
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depth-first,
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emitting events
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as it encounters items.
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By default
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it coerces
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promises, buffers and iterables
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to JSON-friendly values.
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## How do I install it?
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If you're using npm:
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```
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npm i bfj --save
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```
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Or if you just want
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the git repo:
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```
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git clone git@gitlab.com:philbooth/bfj.git
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```
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## How do I read a JSON file?
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```js
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const bfj = require('bfj');
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bfj.read(path, options)
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.then(data => {
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// :)
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})
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.catch(error => {
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// :(
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});
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```
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`read` returns a [bluebird promise][promise] and
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asynchronously parses
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a JSON file
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from disk.
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It takes two arguments;
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the path to the JSON file
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and an [options](#options-for-parsing-functions) object.
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If there are
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no syntax errors,
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the returned promise is resolved
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with the parsed data.
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If syntax errors occur,
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the promise is rejected
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with the first error.
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## How do I parse a stream of JSON?
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```js
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const bfj = require('bfj');
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// By passing a readable stream to bfj.parse():
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bfj.parse(fs.createReadStream(path), options)
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.then(data => {
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// :)
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})
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.catch(error => {
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// :(
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});
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// ...or by passing the result from bfj.unpipe() to stream.pipe():
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request({ url }).pipe(bfj.unpipe((error, data) => {
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if (error) {
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// :(
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} else {
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// :)
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}
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}))
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```
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* `parse` returns a [bluebird promise][promise]
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and asynchronously parses
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a stream of JSON data.
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It takes two arguments;
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a [readable stream][readable]
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from which
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the JSON
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will be parsed
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and an [options](#options-for-parsing-functions) object.
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If there are
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no syntax errors,
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the returned promise is resolved
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with the parsed data.
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If syntax errors occur,
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the promise is rejected
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with the first error.
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* `unpipe` returns a [writable stream][writable]
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that can be passed to [`stream.pipe`][pipe],
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then parses JSON data
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read from the stream.
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It takes two arguments;
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a callback function
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that will be called
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after parsing is complete
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and an [options](#options-for-parsing-functions) object.
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If there are no errors,
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the callback is invoked
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with the result as the second argument.
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If errors occur,
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the first error is passed
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the callback
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as the first argument.
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## How do I selectively parse individual items from a JSON stream?
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```js
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const bfj = require('bfj');
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// Call match with your stream and a selector predicate/regex/string
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const dataStream = bfj.match(jsonStream, selector, options);
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// Get data out of the returned stream with event handlers
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dataStream.on('data', item => { /* ... */ });
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dataStream.on('end', () => { /* ... */);
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dataStream.on('error', () => { /* ... */);
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dataStream.on('dataError', () => { /* ... */);
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// ...or you can pipe it to another stream
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dataStream.pipe(someOtherStream);
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```
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`match` returns a readable, object-mode stream
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and asynchronously parses individual matching items
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from an input JSON stream.
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It takes three arguments:
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a [readable stream][readable]
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from which the JSON will be parsed;
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a selector argument for determining matches,
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which may be a string, a regular expression or a predicate function;
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and an [options](#options-for-parsing-functions) object.
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If the selector is a string,
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it will be compared to property keys
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to determine whether
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each item in the data is a match.
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If it is a regular expression,
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the comparison will be made
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by calling the [RegExp `test` method][regexp-test]
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with the property key.
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Predicate functions will be called with three arguments:
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`key`, `value` and `depth`.
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If the result of the predicate is a truthy value
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then the item will be deemed a match.
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If there are any syntax errors in the JSON,
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a `dataError` event will be emitted.
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If any other errors occur,
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an `error` event will be emitted.
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## How do I write a JSON file?
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```js
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const bfj = require('bfj');
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bfj.write(path, data, options)
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.then(() => {
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// :)
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})
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.catch(error => {
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// :(
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});
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```
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`write` returns a [bluebird promise][promise]
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and asynchronously serialises a data structure
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to a JSON file on disk.
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The promise is resolved
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when the file has been written,
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or rejected with the error
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if writing failed.
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It takes three arguments;
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the path to the JSON file,
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the data structure to serialise
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and an [options](#options-for-serialisation-functions) object.
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## How do I create a stream of JSON?
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```js
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const bfj = require('bfj');
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const stream = bfj.streamify(data, options);
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// Get data out of the stream with event handlers
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stream.on('data', chunk => { /* ... */ });
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stream.on('end', () => { /* ... */);
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stream.on('error', () => { /* ... */);
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stream.on('dataError', () => { /* ... */);
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// ...or you can pipe it to another stream
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stream.pipe(someOtherStream);
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```
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`streamify` returns a [readable stream][readable]
|
||
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and asynchronously serialises
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a data structure to JSON,
|
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pushing the result
|
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to the returned stream.
|
||
|
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|
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It takes two arguments;
|
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the data structure to serialise
|
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and an [options](#options-for-serialisation-functions) object.
|
||
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If there a circular reference is encountered in the data
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and `options.circular` is not set to `'ignore'`,
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a `dataError` event will be emitted.
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If any other errors occur,
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an `error` event will be emitted.
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|
|
|
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|
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## How do I create a JSON string?
|
||
|
|
|
||
|
|
```js
|
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const bfj = require('bfj');
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bfj.stringify(data, options)
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.then(json => {
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// :)
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})
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.catch(error => {
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// :(
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});
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```
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|
|
|
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|
|
`stringify` returns a [bluebird promise][promise] and
|
||
|
|
asynchronously serialises a data structure
|
||
|
|
to a JSON string.
|
||
|
|
The promise is resolved
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||
|
|
to the JSON string
|
||
|
|
when serialisation is complete.
|
||
|
|
|
||
|
|
It takes two arguments;
|
||
|
|
the data structure to serialise
|
||
|
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and an [options](#options-for-serialisation-functions) object.
|
||
|
|
|
||
|
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## What other methods are there?
|
||
|
|
|
||
|
|
### bfj.walk (stream, options)
|
||
|
|
|
||
|
|
```js
|
||
|
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const bfj = require('bfj');
|
||
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|
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const emitter = bfj.walk(fs.createReadStream(path), options);
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emitter.on(bfj.events.array, () => { /* ... */ });
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emitter.on(bfj.events.object, () => { /* ... */ });
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emitter.on(bfj.events.property, name => { /* ... */ });
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emitter.on(bfj.events.string, value => { /* ... */ });
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emitter.on(bfj.events.number, value => { /* ... */ });
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emitter.on(bfj.events.literal, value => { /* ... */ });
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emitter.on(bfj.events.endArray, () => { /* ... */ });
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emitter.on(bfj.events.endObject, () => { /* ... */ });
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emitter.on(bfj.events.error, error => { /* ... */ });
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emitter.on(bfj.events.dataError, error => { /* ... */ });
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|
|
emitter.on(bfj.events.end, () => { /* ... */ });
|
||
|
|
```
|
||
|
|
|
||
|
|
`walk` returns an [event emitter][eventemitter]
|
||
|
|
and asynchronously walks
|
||
|
|
a stream of JSON data,
|
||
|
|
emitting events
|
||
|
|
as it encounters
|
||
|
|
tokens.
|
||
|
|
|
||
|
|
It takes two arguments;
|
||
|
|
a [readable stream][readable]
|
||
|
|
from which
|
||
|
|
the JSON
|
||
|
|
will be read
|
||
|
|
and an [options](#options-for-parsing-functions) object.
|
||
|
|
|
||
|
|
The emitted events
|
||
|
|
are defined
|
||
|
|
as public properties
|
||
|
|
of an object,
|
||
|
|
`bfj.events`:
|
||
|
|
|
||
|
|
* `bfj.events.array`
|
||
|
|
indicates that
|
||
|
|
an array context
|
||
|
|
has been entered
|
||
|
|
by encountering
|
||
|
|
the `[` character.
|
||
|
|
|
||
|
|
* `bfj.events.endArray`
|
||
|
|
indicates that
|
||
|
|
an array context
|
||
|
|
has been left
|
||
|
|
by encountering
|
||
|
|
the `]` character.
|
||
|
|
|
||
|
|
* `bfj.events.object`
|
||
|
|
indicates that
|
||
|
|
an object context
|
||
|
|
has been entered
|
||
|
|
by encountering
|
||
|
|
the `{` character.
|
||
|
|
|
||
|
|
* `bfj.events.endObject`
|
||
|
|
indicates that
|
||
|
|
an object context
|
||
|
|
has been left
|
||
|
|
by encountering
|
||
|
|
the `}` character.
|
||
|
|
|
||
|
|
* `bfj.events.property`
|
||
|
|
indicates that
|
||
|
|
a property
|
||
|
|
has been encountered
|
||
|
|
in an object.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the name of the property
|
||
|
|
as its argument
|
||
|
|
and the next event
|
||
|
|
to be emitted
|
||
|
|
will represent
|
||
|
|
the property's value.
|
||
|
|
|
||
|
|
* `bfj.events.string`
|
||
|
|
indicates that
|
||
|
|
a string
|
||
|
|
has been encountered.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the value
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.number`
|
||
|
|
indicates that
|
||
|
|
a number
|
||
|
|
has been encountered.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the value
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.literal`
|
||
|
|
indicates that
|
||
|
|
a JSON literal
|
||
|
|
(either `true`, `false` or `null`)
|
||
|
|
has been encountered.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the value
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.error`
|
||
|
|
indicates that
|
||
|
|
an error was caught
|
||
|
|
from one of the event handlers
|
||
|
|
in user code.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the `Error` instance
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.dataError`
|
||
|
|
indicates that
|
||
|
|
a syntax error was encountered
|
||
|
|
in the incoming JSON stream.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
an `Error` instance
|
||
|
|
decorated with `actual`, `expected`, `lineNumber` and `columnNumber` properties
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.end`
|
||
|
|
indicates that
|
||
|
|
the end of the input
|
||
|
|
has been reached
|
||
|
|
and the stream is closed.
|
||
|
|
|
||
|
|
* `bfj.events.endLine`
|
||
|
|
indicates that a root-level newline character
|
||
|
|
has been encountered in an [NDJSON](#can-it-handle-newline-delimited-json-ndjson) stream.
|
||
|
|
Only emitted if the `ndjson` [option](#options-for-parsing-functions) is set.
|
||
|
|
|
||
|
|
If you are using `bfj.walk`
|
||
|
|
to sequentially parse items in an array,
|
||
|
|
you might also be interested in
|
||
|
|
the [bfj-collections] module.
|
||
|
|
|
||
|
|
### bfj.eventify (data, options)
|
||
|
|
|
||
|
|
```js
|
||
|
|
const bfj = require('bfj');
|
||
|
|
|
||
|
|
const emitter = bfj.eventify(data, options);
|
||
|
|
|
||
|
|
emitter.on(bfj.events.array, () => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.object, () => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.property, name => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.string, value => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.number, value => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.literal, value => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.endArray, () => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.endObject, () => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.error, error => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.dataError, error => { /* ... */ });
|
||
|
|
emitter.on(bfj.events.end, () => { /* ... */ });
|
||
|
|
```
|
||
|
|
|
||
|
|
`eventify` returns an [event emitter][eventemitter]
|
||
|
|
and asynchronously traverses
|
||
|
|
a data structure depth-first,
|
||
|
|
emitting events as it
|
||
|
|
encounters items.
|
||
|
|
By default it coerces
|
||
|
|
promises, buffers and iterables
|
||
|
|
to JSON-friendly values.
|
||
|
|
|
||
|
|
It takes two arguments;
|
||
|
|
the data structure to traverse
|
||
|
|
and an [options](#options-for-serialisation-functions) object.
|
||
|
|
|
||
|
|
The emitted events
|
||
|
|
are defined
|
||
|
|
as public properties
|
||
|
|
of an object,
|
||
|
|
`bfj.events`:
|
||
|
|
|
||
|
|
* `bfj.events.array`
|
||
|
|
indicates that
|
||
|
|
an array
|
||
|
|
has been encountered.
|
||
|
|
|
||
|
|
* `bfj.events.endArray`
|
||
|
|
indicates that
|
||
|
|
the end of an array
|
||
|
|
has been encountered.
|
||
|
|
|
||
|
|
* `bfj.events.object`
|
||
|
|
indicates that
|
||
|
|
an object
|
||
|
|
has been encountered.
|
||
|
|
|
||
|
|
* `bfj.events.endObject`
|
||
|
|
indicates that
|
||
|
|
the end of an object
|
||
|
|
has been encountered.
|
||
|
|
|
||
|
|
* `bfj.events.property`
|
||
|
|
indicates that
|
||
|
|
a property
|
||
|
|
has been encountered
|
||
|
|
in an object.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the name of the property
|
||
|
|
as its argument
|
||
|
|
and the next event
|
||
|
|
to be emitted
|
||
|
|
will represent
|
||
|
|
the property's value.
|
||
|
|
|
||
|
|
* `bfj.events.string`
|
||
|
|
indicates that
|
||
|
|
a string
|
||
|
|
has been encountered.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the value
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.number`
|
||
|
|
indicates that
|
||
|
|
a number
|
||
|
|
has been encountered.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the value
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.literal`
|
||
|
|
indicates that
|
||
|
|
a JSON literal
|
||
|
|
(either `true`, `false` or `null`)
|
||
|
|
has been encountered.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the value
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.error`
|
||
|
|
indicates that
|
||
|
|
an error was caught
|
||
|
|
from one of the event handlers
|
||
|
|
in user code.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
the `Error` instance
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.dataError`
|
||
|
|
indicates that
|
||
|
|
a circular reference was encountered in the data
|
||
|
|
and the `circular` option was not set to `'ignore'`.
|
||
|
|
The listener
|
||
|
|
will be passed
|
||
|
|
an `Error` instance
|
||
|
|
as its argument.
|
||
|
|
|
||
|
|
* `bfj.events.end`
|
||
|
|
indicates that
|
||
|
|
the end of the data
|
||
|
|
has been reached and
|
||
|
|
no further events
|
||
|
|
will be emitted.
|
||
|
|
|
||
|
|
## What options can I specify?
|
||
|
|
|
||
|
|
### Options for parsing functions
|
||
|
|
|
||
|
|
* `options.reviver`:
|
||
|
|
Transformation function,
|
||
|
|
invoked depth-first
|
||
|
|
against the parsed
|
||
|
|
data structure.
|
||
|
|
This option
|
||
|
|
is analagous to the
|
||
|
|
[reviver parameter for JSON.parse][reviver].
|
||
|
|
|
||
|
|
* `options.yieldRate`:
|
||
|
|
The number of data items to process
|
||
|
|
before yielding to the event loop.
|
||
|
|
Smaller values yield to the event loop more frequently,
|
||
|
|
meaning less time will be consumed by bfj per tick
|
||
|
|
but the overall parsing time will be slower.
|
||
|
|
Larger values yield to the event loop less often,
|
||
|
|
meaning slower tick times but faster overall parsing time.
|
||
|
|
The default value is `16384`.
|
||
|
|
|
||
|
|
* `options.Promise`:
|
||
|
|
Promise constructor that will be used
|
||
|
|
for promises returned by all methods.
|
||
|
|
If you set this option,
|
||
|
|
please be aware that some promise implementations
|
||
|
|
(including native promises)
|
||
|
|
may cause your process to die
|
||
|
|
with out-of-memory exceptions.
|
||
|
|
Defaults to [bluebird's implementation][promise],
|
||
|
|
which does not have that problem.
|
||
|
|
|
||
|
|
* `options.ndjson`:
|
||
|
|
If set to `true`,
|
||
|
|
newline characters at the root level
|
||
|
|
will be treated as delimiters between
|
||
|
|
discrete chunks of JSON.
|
||
|
|
See [NDJSON](#can-it-handle-newline-delimited-json-ndjson) for more information.
|
||
|
|
|
||
|
|
* `options.numbers`:
|
||
|
|
For `bfj.match` only,
|
||
|
|
set this to `true`
|
||
|
|
if you wish to match against numbers
|
||
|
|
with a string or regular expression
|
||
|
|
`selector` argument.
|
||
|
|
|
||
|
|
* `options.bufferLength`:
|
||
|
|
For `bfj.match` only,
|
||
|
|
the length of the match buffer.
|
||
|
|
Smaller values use less memory
|
||
|
|
but may result in a slower parse time.
|
||
|
|
The default value is `1024`.
|
||
|
|
|
||
|
|
* `options.highWaterMark`:
|
||
|
|
For `bfj.match` only,
|
||
|
|
set this if you would like to
|
||
|
|
pass a value for the `highWaterMark` option
|
||
|
|
to the readable stream constructor.
|
||
|
|
|
||
|
|
### Options for serialisation functions
|
||
|
|
|
||
|
|
* `options.space`:
|
||
|
|
Indentation string
|
||
|
|
or the number of spaces
|
||
|
|
to indent
|
||
|
|
each nested level by.
|
||
|
|
This option
|
||
|
|
is analagous to the
|
||
|
|
[space parameter for JSON.stringify][space].
|
||
|
|
|
||
|
|
* `options.promises`:
|
||
|
|
By default,
|
||
|
|
promises are coerced
|
||
|
|
to their resolved value.
|
||
|
|
Set this property
|
||
|
|
to `'ignore'`
|
||
|
|
for improved performance
|
||
|
|
if you don't need
|
||
|
|
to coerce promises.
|
||
|
|
|
||
|
|
* `options.buffers`:
|
||
|
|
By default,
|
||
|
|
buffers are coerced
|
||
|
|
using their `toString` method.
|
||
|
|
Set this property
|
||
|
|
to `'ignore'`
|
||
|
|
for improved performance
|
||
|
|
if you don't need
|
||
|
|
to coerce buffers.
|
||
|
|
|
||
|
|
* `options.maps`:
|
||
|
|
By default,
|
||
|
|
maps are coerced
|
||
|
|
to plain objects.
|
||
|
|
Set this property
|
||
|
|
to `'ignore'`
|
||
|
|
for improved performance
|
||
|
|
if you don't need
|
||
|
|
to coerce maps.
|
||
|
|
|
||
|
|
* `options.iterables`:
|
||
|
|
By default,
|
||
|
|
other iterables
|
||
|
|
(i.e. not arrays, strings or maps)
|
||
|
|
are coerced
|
||
|
|
to arrays.
|
||
|
|
Set this property
|
||
|
|
to `'ignore'`
|
||
|
|
for improved performance
|
||
|
|
if you don't need
|
||
|
|
to coerce iterables.
|
||
|
|
|
||
|
|
* `options.circular`:
|
||
|
|
By default,
|
||
|
|
circular references
|
||
|
|
will cause the write
|
||
|
|
to fail.
|
||
|
|
Set this property
|
||
|
|
to `'ignore'`
|
||
|
|
if you'd prefer
|
||
|
|
to silently skip past
|
||
|
|
circular references
|
||
|
|
in the data.
|
||
|
|
|
||
|
|
* `options.bufferLength`:
|
||
|
|
The length of the write buffer.
|
||
|
|
Smaller values use less memory
|
||
|
|
but may result in a slower serialisation time.
|
||
|
|
The default value is `1024`.
|
||
|
|
|
||
|
|
* `options.highWaterMark`:
|
||
|
|
Set this if you would like to
|
||
|
|
pass a value for the `highWaterMark` option
|
||
|
|
to the readable stream constructor.
|
||
|
|
|
||
|
|
* `options.yieldRate`:
|
||
|
|
The number of data items to process
|
||
|
|
before yielding to the event loop.
|
||
|
|
Smaller values yield to the event loop more frequently,
|
||
|
|
meaning less time will be consumed by bfj per tick
|
||
|
|
but the overall serialisation time will be slower.
|
||
|
|
Larger values yield to the event loop less often,
|
||
|
|
meaning slower tick times but faster overall serialisation time.
|
||
|
|
The default value is `16384`.
|
||
|
|
|
||
|
|
* `options.Promise`:
|
||
|
|
Promise constructor that will be used
|
||
|
|
for promises returned by all methods.
|
||
|
|
If you set this option,
|
||
|
|
please be aware that some promise implementations
|
||
|
|
(including native promises)
|
||
|
|
may cause your process to die
|
||
|
|
with out-of-memory exceptions.
|
||
|
|
Defaults to [bluebird's implementation][promise],
|
||
|
|
which does not have that problem.
|
||
|
|
|
||
|
|
## Is it possible to pause parsing or serialisation from calling code?
|
||
|
|
|
||
|
|
Yes it is!
|
||
|
|
Both [`walk`](#bfjwalk-stream-options)
|
||
|
|
and [`eventify`](#bfjeventify-data-options)
|
||
|
|
decorate their returned event emitters
|
||
|
|
with a `pause` method
|
||
|
|
that will prevent any further events being emitted.
|
||
|
|
The `pause` method itself
|
||
|
|
returns a `resume` function
|
||
|
|
that you can call to indicate
|
||
|
|
that processing should continue.
|
||
|
|
|
||
|
|
For example:
|
||
|
|
|
||
|
|
```js
|
||
|
|
const bfj = require('bfj');
|
||
|
|
const emitter = bfj.walk(fs.createReadStream(path), options);
|
||
|
|
|
||
|
|
// Later, when you want to pause parsing:
|
||
|
|
|
||
|
|
const resume = emitter.pause();
|
||
|
|
|
||
|
|
// Then when you want to resume:
|
||
|
|
|
||
|
|
resume();
|
||
|
|
```
|
||
|
|
|
||
|
|
## Can it handle [newline-delimited JSON (NDJSON)](http://ndjson.org/)?
|
||
|
|
|
||
|
|
Yes.
|
||
|
|
If you pass the `ndjson` [option](#options-for-parsing-functions)
|
||
|
|
to `bfj.walk`, `bfj.match` or `bfj.parse`,
|
||
|
|
newline characters at the root level
|
||
|
|
will act as delimiters between
|
||
|
|
discrete JSON values:
|
||
|
|
|
||
|
|
* `bfj.walk` will emit a `bfj.events.endLine` event
|
||
|
|
each time it encounters a newline character.
|
||
|
|
|
||
|
|
* `bfj.match` will just ignore the newlines
|
||
|
|
while it continues looking for matching items.
|
||
|
|
|
||
|
|
* `bfj.parse` will resolve with the first value
|
||
|
|
and pause the underlying stream.
|
||
|
|
If it's called again with the same stream,
|
||
|
|
it will resume processing
|
||
|
|
and resolve with the second value.
|
||
|
|
To parse the entire stream,
|
||
|
|
calls should be made sequentially one-at-a-time
|
||
|
|
until the returned promise
|
||
|
|
resolves to `undefined`
|
||
|
|
(`undefined` is not a valid JSON token).
|
||
|
|
|
||
|
|
`bfj.unpipe` and `bfj.read` will not parse NDJSON.
|
||
|
|
|
||
|
|
## Why does it default to bluebird promises?
|
||
|
|
|
||
|
|
Until version `4.2.4`,
|
||
|
|
native promises were used.
|
||
|
|
But they were found
|
||
|
|
to cause out-of-memory errors
|
||
|
|
when serialising large amounts of data to JSON,
|
||
|
|
due to [well-documented problems
|
||
|
|
with the native promise implementation](https://alexn.org/blog/2017/10/11/javascript-promise-leaks-memory.html).
|
||
|
|
So in version `5.0.0`,
|
||
|
|
bluebird promises were used instead.
|
||
|
|
In version `5.1.0`,
|
||
|
|
an option was added
|
||
|
|
that enables callers to specify
|
||
|
|
the promise constructor to use.
|
||
|
|
Use it at your own risk.
|
||
|
|
|
||
|
|
## Can I specify a different promise implementation?
|
||
|
|
|
||
|
|
Yes.
|
||
|
|
Just pass the `Promise` option
|
||
|
|
to any method.
|
||
|
|
If you get out-of-memory errors
|
||
|
|
when using that option,
|
||
|
|
consider changing your promise implementation.
|
||
|
|
|
||
|
|
## Is there a change log?
|
||
|
|
|
||
|
|
[Yes][history].
|
||
|
|
|
||
|
|
## How do I set up the dev environment?
|
||
|
|
|
||
|
|
The development environment
|
||
|
|
relies on [Node.js][node],
|
||
|
|
[ESLint],
|
||
|
|
[Mocha],
|
||
|
|
[Chai],
|
||
|
|
[Proxyquire] and
|
||
|
|
[Spooks].
|
||
|
|
Assuming that
|
||
|
|
you already have
|
||
|
|
node and NPM
|
||
|
|
set up,
|
||
|
|
you just need
|
||
|
|
to run
|
||
|
|
`npm install`
|
||
|
|
to install
|
||
|
|
all of the dependencies
|
||
|
|
as listed in `package.json`.
|
||
|
|
|
||
|
|
You can
|
||
|
|
lint the code
|
||
|
|
with the command
|
||
|
|
`npm run lint`.
|
||
|
|
|
||
|
|
You can
|
||
|
|
run the tests
|
||
|
|
with the command
|
||
|
|
`npm test`.
|
||
|
|
|
||
|
|
## What versions of Node.js does it support?
|
||
|
|
|
||
|
|
As of [version `3.0.0`](HISTORY.md#300),
|
||
|
|
only Node.js versions 6 or greater
|
||
|
|
are supported
|
||
|
|
because of the dependency
|
||
|
|
on [Hoopy](https://gitlab.com/philbooth/hoopy).
|
||
|
|
Previous versions supported
|
||
|
|
node 4 and later.
|
||
|
|
|
||
|
|
A separate `node-4` branch was maintained
|
||
|
|
until version `5.4.1`,
|
||
|
|
which had feature parity version-for-version
|
||
|
|
with releases from `master`.
|
||
|
|
Releases from the `node-4` branch
|
||
|
|
are available in npm
|
||
|
|
under the package name [`bfj-node4`](https://www.npmjs.com/package/bfj-node4).
|
||
|
|
|
||
|
|
## What license is it released under?
|
||
|
|
|
||
|
|
[MIT][license].
|
||
|
|
|
||
|
|
[ci-image]: https://secure.travis-ci.org/philbooth/bfj.png?branch=master
|
||
|
|
[ci-status]: http://travis-ci.org/#!/philbooth/bfj
|
||
|
|
[sax]: http://en.wikipedia.org/wiki/Simple_API_for_XML
|
||
|
|
[promise]: http://bluebirdjs.com/docs/api-reference.html
|
||
|
|
[bfj-collections]: https://github.com/hash-bang/bfj-collections
|
||
|
|
[eventemitter]: https://nodejs.org/api/events.html#events_class_eventemitter
|
||
|
|
[readable]: https://nodejs.org/api/stream.html#stream_readable_streams
|
||
|
|
[writable]: https://nodejs.org/api/stream.html#stream_writable_streams
|
||
|
|
[pipe]: https://nodejs.org/api/stream.html#stream_readable_pipe_destination_options
|
||
|
|
[regexp-test]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/test
|
||
|
|
[reviver]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse#Using_the_reviver_parameter
|
||
|
|
[space]: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#The_space_argument
|
||
|
|
[history]: HISTORY.md
|
||
|
|
[node]: https://nodejs.org/en/
|
||
|
|
[eslint]: http://eslint.org/
|
||
|
|
[mocha]: https://mochajs.org/
|
||
|
|
[chai]: http://chaijs.com/
|
||
|
|
[proxyquire]: https://github.com/thlorenz/proxyquire
|
||
|
|
[spooks]: https://gitlab.com/philbooth/spooks.js
|
||
|
|
[license]: COPYING
|