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# JSONStream streaming JSON.parse and stringify  ## install ```npm install JSONStream``` ## 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 })) ``` ## JSONStream.parse(path) parse stream of values that match a path ``` js JSONStream.parse('rows.*.doc') ``` The `..` operator is the recursive descent operator from [JSONPath](http://goessner.net/articles/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. ### Examples query a couchdb view: ``` bash curl -sS localhost:5984/tests/_all_docs&include_docs=true ``` you will get something like this: ``` js {"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: ``` js 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: ``` js 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: ``` js 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); }); ``` ### recursive patterns (..) `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. ```js { "total": 5, "docs": [ { "key": { "value": 0, "some": "property" } }, {"value": 1}, {"value": 2}, {"blbl": [{}, {"a":0, "b":1, "value":3}, 10]}, {"value": 4} ] } ``` ## JSONStream.parse(pattern, map) 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. ## JSONStream.stringify(open, sep, close) 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. ## JSONStream.stringifyObject(open, sep, close) 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. ## unix tool query npm to see all the modules that browserify has ever depended on. ``` bash curl https://registry.npmjs.org/browserify | JSONStream 'versions.*.dependencies' ``` ## numbers 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. ## Acknowlegements 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 ## license Dual-licensed under the MIT License or the Apache License, version 2.0
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