.. | ||
src | ||
test | ||
.eslintrc | ||
.gitlab-ci.yml | ||
AUTHORS | ||
CONTRIBUTING.md | ||
COPYING | ||
HISTORY.md | ||
package.json | ||
README.md |
BFJ
Big-Friendly JSON. Asynchronous streaming functions for large JSON data sets.
- Why would I want those?
- Is it fast?
- What functions does it implement?
- How do I install it?
- How do I read a JSON file?
- How do I parse a stream of JSON?
- How do I selectively parse individual items from a JSON stream?
- How do I write a JSON file?
- How do I create a stream of JSON?
- How do I create a JSON string?
- What other methods are there?
- What options can I specify?
- Is it possible to pause parsing or serialisation from calling code?
- Can it handle newline-delimited JSON (NDJSON)?
- Why does it default to bluebird promises?
- Can I specify a different promise implementation?
- Is there a change log?
- How do I set up the dev environment?
- What versions of Node.js does it support?
- What license is it released under?
Why would I want those?
If you need to parse huge JSON strings or stringify huge JavaScript data sets, it monopolises the event loop and can lead to out-of-memory exceptions. BFJ implements asynchronous functions and uses pre-allocated fixed-length arrays to try and alleviate those issues.
Is it fast?
No.
BFJ yields frequently
to avoid monopolising the event loop,
interrupting its own execution
to let other event handlers run.
The frequency of those yields
can be controlled with the yieldRate
option,
but fundamentally it is not designed for speed.
Furthermore,
when serialising data to a stream,
BFJ uses a fixed-length buffer
to avoid exhausting available memory.
Whenever that buffer is full,
serialisation is paused
until the receiving stream processes some more data,
regardless of the value of yieldRate
.
You can control the size of the buffer
using the bufferLength
option
but really,
if you need quick results,
BFJ is not for you.
What functions does it implement?
Nine functions are exported.
Five are concerned with parsing, or turning JSON strings into JavaScript data:
-
read
asynchronously parses a JSON file from disk. -
parse
andunpipe
are for asynchronously parsing streams of JSON. -
match
selectively parses individual items from a JSON stream. -
walk
asynchronously walks a stream, emitting events as it encounters JSON tokens. Analagous to a SAX parser.
The other four functions handle the reverse transformations, serialising JavaScript data to JSON:
-
write
asynchronously serialises data to a JSON file on disk. -
streamify
asynchronously serialises data to a stream of JSON. -
stringify
asynchronously serialises data to a JSON string. -
eventify
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.
How do I install it?
If you're using npm:
npm i bfj --save
Or if you just want the git repo:
git clone git@gitlab.com:philbooth/bfj.git
How do I read a JSON file?
const bfj = require('bfj');
bfj.read(path, options)
.then(data => {
// :)
})
.catch(error => {
// :(
});
read
returns a bluebird promise and
asynchronously parses
a JSON file
from disk.
It takes two arguments; the path to the JSON file and an options object.
If there are no syntax errors, the returned promise is resolved with the parsed data. If syntax errors occur, the promise is rejected with the first error.
How do I parse a stream of JSON?
const bfj = require('bfj');
// By passing a readable stream to bfj.parse():
bfj.parse(fs.createReadStream(path), options)
.then(data => {
// :)
})
.catch(error => {
// :(
});
// ...or by passing the result from bfj.unpipe() to stream.pipe():
request({ url }).pipe(bfj.unpipe((error, data) => {
if (error) {
// :(
} else {
// :)
}
}))
-
parse
returns a bluebird promise and asynchronously parses a stream of JSON data.It takes two arguments; a readable stream from which the JSON will be parsed and an options object.
If there are no syntax errors, the returned promise is resolved with the parsed data. If syntax errors occur, the promise is rejected with the first error.
-
unpipe
returns a writable stream that can be passed tostream.pipe
, then parses JSON data read from the stream.It takes two arguments; a callback function that will be called after parsing is complete and an options object.
If there are no errors, the callback is invoked with the result as the second argument. If errors occur, the first error is passed the callback as the first argument.
How do I selectively parse individual items from a JSON stream?
const bfj = require('bfj');
// Call match with your stream and a selector predicate/regex/string
const dataStream = bfj.match(jsonStream, selector, options);
// Get data out of the returned stream with event handlers
dataStream.on('data', item => { /* ... */ });
dataStream.on('end', () => { /* ... */);
dataStream.on('error', () => { /* ... */);
dataStream.on('dataError', () => { /* ... */);
// ...or you can pipe it to another stream
dataStream.pipe(someOtherStream);
match
returns a readable, object-mode stream
and asynchronously parses individual matching items
from an input JSON stream.
It takes three arguments: a readable stream from which the JSON will be parsed; a selector argument for determining matches, which may be a string, a regular expression or a predicate function; and an options object.
If the selector is a string,
it will be compared to property keys
to determine whether
each item in the data is a match.
If it is a regular expression,
the comparison will be made
by calling the RegExp test
method
with the property key.
Predicate functions will be called with three arguments:
key
, value
and depth
.
If the result of the predicate is a truthy value
then the item will be deemed a match.
If there are any syntax errors in the JSON,
a dataError
event will be emitted.
If any other errors occur,
an error
event will be emitted.
How do I write a JSON file?
const bfj = require('bfj');
bfj.write(path, data, options)
.then(() => {
// :)
})
.catch(error => {
// :(
});
write
returns a bluebird promise
and asynchronously serialises a data structure
to a JSON file on disk.
The promise is resolved
when the file has been written,
or rejected with the error
if writing failed.
It takes three arguments; the path to the JSON file, the data structure to serialise and an options object.
How do I create a stream of JSON?
const bfj = require('bfj');
const stream = bfj.streamify(data, options);
// Get data out of the stream with event handlers
stream.on('data', chunk => { /* ... */ });
stream.on('end', () => { /* ... */);
stream.on('error', () => { /* ... */);
stream.on('dataError', () => { /* ... */);
// ...or you can pipe it to another stream
stream.pipe(someOtherStream);
streamify
returns a readable stream
and asynchronously serialises
a data structure to JSON,
pushing the result
to the returned stream.
It takes two arguments; the data structure to serialise and an options object.
If there a circular reference is encountered in the data
and options.circular
is not set to 'ignore'
,
a dataError
event will be emitted.
If any other errors occur,
an error
event will be emitted.
How do I create a JSON string?
const bfj = require('bfj');
bfj.stringify(data, options)
.then(json => {
// :)
})
.catch(error => {
// :(
});
stringify
returns a bluebird promise and
asynchronously serialises a data structure
to a JSON string.
The promise is resolved
to the JSON string
when serialisation is complete.
It takes two arguments; the data structure to serialise and an options object.
What other methods are there?
bfj.walk (stream, options)
const bfj = require('bfj');
const emitter = bfj.walk(fs.createReadStream(path), 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, () => { /* ... */ });
walk
returns an event emitter
and asynchronously walks
a stream of JSON data,
emitting events
as it encounters
tokens.
It takes two arguments; a readable stream from which the JSON will be read and an options 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 (eithertrue
,false
ornull
) 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 theError
instance as its argument. -
bfj.events.dataError
indicates that a syntax error was encountered in the incoming JSON stream. The listener will be passed anError
instance decorated withactual
,expected
,lineNumber
andcolumnNumber
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 stream. Only emitted if thendjson
option 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)
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
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 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 (eithertrue
,false
ornull
) 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 theError
instance as its argument. -
bfj.events.dataError
indicates that a circular reference was encountered in the data and thecircular
option was not set to'ignore'
. The listener will be passed anError
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. -
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 is16384
. -
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, which does not have that problem. -
options.ndjson
: If set totrue
, newline characters at the root level will be treated as delimiters between discrete chunks of JSON. See NDJSON for more information. -
options.numbers
: Forbfj.match
only, set this totrue
if you wish to match against numbers with a string or regular expressionselector
argument. -
options.bufferLength
: Forbfj.match
only, the length of the match buffer. Smaller values use less memory but may result in a slower parse time. The default value is1024
. -
options.highWaterMark
: Forbfj.match
only, set this if you would like to pass a value for thehighWaterMark
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. -
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 theirtoString
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 is1024
. -
options.highWaterMark
: Set this if you would like to pass a value for thehighWaterMark
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 is16384
. -
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, which does not have that problem.
Is it possible to pause parsing or serialisation from calling code?
Yes it is!
Both walk
and eventify
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:
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)?
Yes.
If you pass the ndjson
option
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 abfj.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 toundefined
(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.
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.
How do I set up the dev environment?
The development environment
relies on Node.js,
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
,
only Node.js versions 6 or greater
are supported
because of the dependency
on 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
.
What license is it released under?
MIT.