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Text of the page (random words):
mber 2017 iso iec jtc 1 sc 22 published iso iec 21778 2017 2 as an international standard on december 13 2017 the internet engineering task force obsoleted rfc 7159 when it published rfc 8259 which is the current version of the internet standard std 90 6 crockford added a clause to the json license stating the software shall be used for good not evil in order to open source the json libraries while mocking corporate lawyers and those who are overly pedantic on the other hand this clause led to license compatibility problems of the json license with other open source licenses since open source software and free software usually imply no restrictions on the purpose of use 12 syntax edit the following example shows a possible json representation describing a person first_name john last_name smith is_alive true age 27 address street_address 21 2nd street city new york state ny postal_code 10021 3100 phone_numbers type home number 212 555 1234 type office number 646 555 4567 children catherine thomas trevor spouse null character encoding edit although crockford originally asserted that json is a strict subset of javascript and ecmascript 13 their specification actually allows valid json documents that are not valid javascript json allows the unicode line terminators u 2028 line separator and u 2029 paragraph separator to appear unescaped in quoted strings while ecmascript 2018 and older do not 14 15 this is a consequence of json disallowing only control characters for maximum portability these characters are backslash escaped json exchange in an open ecosystem must be encoded in utf 8 6 the encoding supports the full unicode character set including those characters outside the basic multilingual plane u 0000 to u ffff however if escaped those characters must be written using utf 16 surrogate pairs for example to include the emoji character u 1f610 neutral face in json face or face ud83d ude10 json became a strict subset of ecmascript as of the language s 2019 revision 15 16 data types edit json s basic data types are number a signed decimal number that may contain a fractional part and may use exponential e notation but cannot include non numbers such as nan the format makes no distinction between integer and floating point javascript uses ieee 754 double precision floating point format for all its numeric values later also supporting bigint 17 but other languages implementing json may encode numbers differently string a sequence of zero or more unicode characters strings are delimited with double quotation marks and support a backslash escaping syntax boolean either of the values true or false array an ordered list of zero or more elements each of which may be of any type arrays use square bracket notation with comma separated elements object a collection of name value pairs where the names also called keys are strings the current ecma standard states the json syntax does not impose any restrictions on the strings used as names does not require that name strings be unique and does not assign any significance to the ordering of name value pairs 18 objects are delimited with curly brackets and use commas to separate each pair while within each pair the colon character separates the key or name from its value null an empty value using the word null whitespace is allowed and ignored around or between syntactic elements values and punctuation but not within a string value four specific characters are considered whitespace for this purpose space horizontal tab line feed and carriage return in particular the byte order mark must not be generated by a conforming implementation though it may be accepted when parsing json 19 20 early versions of json such as specified by rfc 4627 required that a valid json text must consist of only an object or an array type which could contain other types within them this restriction was dropped in rfc 7158 where a json text was redefined as any serialized value numbers in json are agnostic with regard to their representation within programming languages while this allows for numbers of arbitrary precision to be serialized it may lead to portability issues for example since no differentiation is made between integer and floating point values some implementations may treat 42 42 0 and 4 2e 1 as the same number while others may not the json standard makes no requirements regarding implementation details such as overflow underflow loss of precision rounding or signed zeros but it does recommend expecting no more than ieee 754 binary64 precision for good interoperability there is no inherent precision loss in serializing a machine level binary representation of a floating point number like binary64 into a human readable decimal representation like numbers in json and back there exist published algorithms to do this conversion exactly and optimally 21 comments edit json does not provide syntax for comments 22 comments were intentionally excluded from json in 2012 douglas crockford described their design decision thus i removed comments from json because i saw people were using them to hold parsing directives a practice which would have destroyed interoperability 22 lint edit json disallows trailing commas a comma after the last value inside a data structure 23 trailing commas are a common feature of json derivatives to improve ease of use 24 interoperability edit rfc 8259 describes certain aspects of json syntax that while legal per the specifications can cause interoperability problems certain json implementations only accept json texts representing an object or an array for interoperability applications interchanging json should transmit messages that are objects or arrays the specifications allow json objects that contain multiple members with the same name the behavior of implementations processing objects with duplicate names is unpredictable for interoperability applications should avoid duplicate names when transmitting json objects the specifications specifically say that the order of members in json objects is not significant for interoperability applications should avoid assigning meaning to member ordering even if the parsing software makes that ordering visible while the specifications place no limits on the magnitude or precision of json number literals the widely used javascript implementation stores them as ieee754 binary64 quantities for interoperability applications should avoid transmitting numbers that cannot be represented in this way for example 1e400 or 3 141592653589793238462643383279 earlier ietf specifications for json did not require utf 8 but rfc 8259 requires json text exchanged between systems that are not part of a closed ecosystem to be encoded in utf 8 the specifications do not forbid transmitting byte sequences that incorrectly represent unicode characters for interoperability applications should transmit messages containing no such byte sequences the specification does not constrain how applications go about comparing unicode strings for interoperability applications should always perform such comparisons code unit by code unit in 2015 the ietf published rfc 7493 describing the i json message format a restricted profile of json that constrains the syntax and processing of json to avoid as much as possible these interoperability issues semantics edit while json provides a syntactic framework for data interchange unambiguous data interchange also requires agreement between producer and consumer on the semantics of specific use of the json syntax 25 one example of where such an agreement is necessary is the serialization of data types that are not part of the json standard for example dates and regular expressions metadata and schema edit the official mime type for json text is application json 26 and most modern implementations have adopted this legacy mime types include text json text x json and text javascript 27 the standard filename extension is json 28 json schema specifies a json based format to define the structure of json data for validation documentation and interaction control it provides a contract for the json data required by a given application and how that data can be modified 29 json schema is based on the concepts from xml schema xsd but is json based as in xsd the same serialization deserialization tools can be used both for the schema and data and it is self describing it is specified in an internet draft at the ietf with the latest version as of 2024 being draft 2020 12 30 there are several validators available for different programming languages 31 each with varying levels of conformance the json standard does not support object references but an ietf draft standard for json based object references exists 32 uses edit json rpc is a remote procedure call rpc protocol built on json as a replacement for xml rpc or soap it is a simple protocol that defines only a handful of data types and commands json rpc lets a system send notifications information to the server that does not require a response and multiple calls to the server that can be answered out of order asynchronous javascript and json or ajaj refers to the same dynamic web page methodology as ajax but instead of xml json is the data format ajaj is a web development technique that provides for the ability of a web page to request new data after it has loaded into the web browser typically it renders new data from the server in response to user actions on that web page for example what the user types into a search box client side code then sends to the server which immediately responds with a drop down list of matching database items json has seen ad hoc usage as a configuration language despite lacking native support for comments see comments mongodb uses json like data for its document oriented database some relational databases have added support for native json data types such as jsonb in postgresql 33 and json in mysql 34 this allows developers to insert json data directly without having to convert it to another format safety edit json being a subset of javascript can lead to the misconception that it is safe to pass json texts to the javascript eval function this is not safe due to certain valid json texts specifically those containing u 2028 line separator or u 2029 paragraph separator not being valid javascript code until javascript specifications were updated in 2019 and so older engines may not support it 14 to avoid the many pitfalls caused by executing arbitrary code from the internet a new function json parse was first added to the fifth edition of ecmascript 35 which as of 2017 is supported by all major browsers for non supported browsers an api compatible javascript library is provided by douglas crockford 36 in addition the tc39 proposal subsume json made ecmascript a strict json superset as of the language s 2019 revision 15 16 various json parser implementations have suffered from denial of service attack and mass assignment vulnerability 37 38 alternatives edit see also comparison of data serialization formats json is promoted as a low overhead alternative to xml as both of these formats have widespread support for creation reading and decoding in the real world situations where they are commonly used 39 depending on the specific use case json alternatives include for textual formats csv and supersets of json see below ion also offers a textual format that s a json superset wider range of primary types annotations comments and allowing trailing commas 40 for faster processing at the cost of human readability data interchange formats that can express all json objects i e that have a data model that is a superset of json s include cbor an ietf rfc standard and ion binary 40 google protocol buffers can also fill this niche due to the ability to be parsed without a schema but it is not intended as an interchange language in addition databases such as sqlite and postgresql have their own internal binary representations called jsonb not intended for outside use 41 xml edit main article xml xml has been used to describe structured data and to serialize objects various xml based protocols exist to represent the same kind of data structures as json for the same kind of data interchange purposes data can be encoded in xml in several ways the most expansive form using tag pairs results in a much larger in character count representation than json but if data is stored in attributes and short tag form where the closing tag is replaced with the representation is often about the same size as json or just a little larger 42 however an xml attribute can only have a single value and each attribute can appear at most once on each element xml separates data from metadata via the use of elements and attributes while json does not have such a concept another key difference is the addressing of values json has objects with a simple key to value mapping whereas in xml addressing happens on nodes each of which receives a unique id via the xml processor additionally the xml standard defines a common attribute xml id that can be used by the user to set an id explicitly xml tag names cannot contain any of the characters nor a space character and cannot begin with or a numeric digit whereas json keys can even if quotation mark and backslash must be escaped 43 xml values are strings of characters with no built in type safety xml has the concept of schema that permits strong typing user defined types predefined tags and formal structure allowing for formal validation of an xml stream json has several types built in and has a similar schema concept in json schema xml supports comments while json does not 44 22 supersets edit support for comments and other features have been deemed useful which has led to several nonstandard json supersets being created among them are hjson 45 hocon and json5 which despite its name is not the fifth version of json 46 47 yaml edit see also yaml json yaml version 1 2 is a superset of json prior versions were not strictly compatible for example escaping a slash with a backslash is valid in json but was not valid in yaml 48 yaml supports comments while json does not 48 46 22 cson edit cson coffeescript object notation uses significant indentation and unquoted keys and assumes an outer object declaration it was used for configuring github s atom text editor 49 50 51 there is also an unrelated project called cson cursive script object notation that is more syntactically similar to json 52 hocon edit hocon human optimized config object notation is a format for human readable data and a superset of json 53 the uses of hocon are it is used mostly along with the play framework 54 and is developed by lightbend it is also supported as a configuration format for net projects via akka net 55 56 and puppet 57 tibco streaming 58 hocon is the primary configuration file format for the tibco streaming 59 family of products streambase liveview and artifact management server as of tibco str...
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