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streaming JSON.parse and stringify
## example
``` js
var request = require('request')
, JSONStream = require('JSONStream')
, es = require('event-stream')
request({url: 'http://isaacs.couchone.com/registry/_all_docs'})
.pipe(JSONStream.parse('rows.*'))
.pipe(es.mapSync(function (data) {
console.error(data)
return data
}))
parse stream of values that match a path
JSONStream.parse('rows.*.doc')
The ..
operator is the recursive descent operator from JSONPath, which will match a child at any depth (see examples below).
If your keys have keys that include .
or *
etc, use an array instead.
['row', true, /^doc/]
.
If you use an array, RegExp
s, booleans, and/or functions. The ..
operator is also available in array representation, using {recurse: true}
.
any object that matches the path will be emitted as 'data' (and pipe
d down stream)
If path
is empty or null, no 'data' events are emitted.
If you want to have keys emitted, you can prefix your *
operator with $
: obj.$*
- in this case the data passed to the stream is an object with a key
holding the key and a value
property holding the data.
query a couchdb view:
curl -sS localhost:5984/tests/_all_docs&include_docs=true
you will get something like this:
{"total_rows":129,"offset":0,"rows":[
{ "id":"change1_0.6995461115147918"
, "key":"change1_0.6995461115147918"
, "value":{"rev":"1-e240bae28c7bb3667f02760f6398d508"}
, "doc":{
"_id": "change1_0.6995461115147918"
, "_rev": "1-e240bae28c7bb3667f02760f6398d508","hello":1}
},
{ "id":"change2_0.6995461115147918"
, "key":"change2_0.6995461115147918"
, "value":{"rev":"1-13677d36b98c0c075145bb8975105153"}
, "doc":{
"_id":"change2_0.6995461115147918"
, "_rev":"1-13677d36b98c0c075145bb8975105153"
, "hello":2
}
},
]}
we are probably most interested in the rows.*.doc
create a Stream
that parses the documents from the feed like this:
var stream = JSONStream.parse(['rows', true, 'doc']) //rows, ANYTHING, doc
stream.on('data', function(data) {
console.log('received:', data);
});
//emits anything from _before_ the first match
stream.on('header', function (data) {
console.log('header:', data) // => {"total_rows":129,"offset":0}
})
awesome!
In case you wanted the contents the doc emitted:
var stream = JSONStream.parse(['rows', true, 'doc', {emitKey: true}]) //rows, ANYTHING, doc, items in docs with keys
stream.on('data', function(data) {
console.log('key:', data.key);
console.log('value:', data.value);
});
You can also emit the path:
var stream = JSONStream.parse(['rows', true, 'doc', {emitPath: true}]) //rows, ANYTHING, doc, items in docs with keys
stream.on('data', function(data) {
console.log('path:', data.path);
console.log('value:', data.value);
});
JSONStream.parse('docs..value')
(or JSONStream.parse(['docs', {recurse: true}, 'value'])
using an array)
will emit every value
object that is a child, grand-child, etc. of the
docs
object. In this example, it will match exactly 5 times at various depth
levels, emitting 0, 1, 2, 3 and 4 as results.
{
"total": 5,
"docs": [
{
"key": {
"value": 0,
"some": "property"
}
},
{"value": 1},
{"value": 2},
{"blbl": [{}, {"a":0, "b":1, "value":3}, 10]},
{"value": 4}
]
}
provide a function that can be used to map or filter
the json output. map
is passed the value at that node of the pattern,
if map
return non-nullish (anything but null
or undefined
)
that value will be emitted in the stream. If it returns a nullish value,
nothing will be emitted.
JSONStream
also emits 'header'
and 'footer'
events,
the 'header'
event contains anything in the output that was before
the first match, and the 'footer'
, is anything after the last match.
Create a writable stream.
you may pass in custom open
, close
, and seperator
strings.
But, by default, JSONStream.stringify()
will create an array,
(with default options open='[\n', sep='\n,\n', close='\n]\n'
)
If you call JSONStream.stringify(false)
the elements will only be seperated by a newline.
If you only write one item this will be valid JSON.
If you write many items,
you can use a RegExp
to split it into valid chunks.
Very much like JSONStream.stringify
,
but creates a writable stream for objects instead of arrays.
Accordingly, open='{\n', sep='\n,\n', close='\n}\n'
.
When you .write()
to the stream you must supply an array with [ key, data ]
as the first argument.
query npm to see all the modules that browserify has ever depended on.
curl https://registry.npmjs.org/browserify | JSONStream 'versions.*.dependencies'
numbers will be emitted as numbers. huge numbers that cannot be represented in memory as javascript numbers will be emitted as strings. cf https://github.com/creationix/jsonparse/commit/044b268f01c4b8f97fb936fc85d3bcfba179e5bb for details.
this module depends on https://github.com/creationix/jsonparse by Tim Caswell and also thanks to Florent Jaby for teaching me about parsing with: https://github.com/Floby/node-json-streams
Dual-licensed under the MIT License or the Apache License, version 2.0