JSON: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: JSON

New		Line
1	+	## Overview
2	+
3	+	[JSON](http://www.json.org) (JavaScript Object Notation) is a form of data representation that provides a standardised data exchange format using simple text. As the name suggests, it is based on a subset of the [[JavaScript]] programming language; however, it is completely language-agnostic. Besides being easy for humans to read and write, it is also easy for machines to parse and generate.
4	+
5	+	Compared to [[XML]], it is more human-readable.
6	+
7	+	## JSON Object
8	+
9	+	A JSON Object is nothing more than a collection of comma-separated name/value pairs (often called members) enclosed in curly brackets:
10	+
11	+	``` javascript
12	+	{"name1":value1, "name2":value2 ...}
13	+	```
14	+
15	+	To make it easier for humans to read and visualize, the name/value pairs are often listed vertically:
16	+
17	+	``` javascript
18	+	{
19	+	"name1": value1,
20	+	"name2": value2
21	+	}
22	+	```
23	+
24	+	The name is supposed to be a string in double quotes, while the value can be any of the following:
25	+
26	+	- a simple string, numeric, boolean or null value (strings are enclosed in double quotes):\
27	+	`{"id":1, "name":"John Doe", "married":false}`
28	+
29	+	- an array; which is a collection of comma-separated values in square brackets:\
30	+	`{"primeNumbers":[2, 3, 5, 7, 11, 13, 17], "oddNumbers":[1,3,5,7]}`
31	+
32	+	- an object; which is a collection of name:value pairs enclosed in curly brackets:\
33	+	`{"address":{"street":"145 Koinange Street", "City":"Nairobi", "Country":"Kenya"}}`
34	+
35	+	JSON objects can always be nested arbitrarily to create even more complex objects:
36	+
37	+	``` javascript
38	+	{"user":
39	+	{ "userid": 1900,
40	+	"username": "jsmith",
41	+	"password": "secret",
42	+	"groups": [ "admins", "users", "maintainers"]
43	+	}
44	+	}
45	+	```
46	+
47	+	Check this [[fcl-json\|link]] for extracting the information when you have several users.
48	+
49	+	## Valid JSON format
50	+
51	+	There are a few rules and guidelines that define the JSON syntax (see RFC 4627):
52	+
53	+	- JSON objects are encapsulated within opening and closing brackets `{ }`. An empty object can be represented by `{ }`
54	+	- Arrays are encapsulated within opening and closing square brackets `[ ]`. An empty array can be represented by `[ ]`
55	+	- A member is represented by a key-value pair
56	+	- The key of a member should be contained in double quotes
57	+	- Each member SHOULD have a unique key within an object structure
58	+	- The value of a member must be contained in double quotes if it is a string
59	+	- Boolean values are represented using the true or false literals in lower case
60	+	- Number values are represented using double-precision floating-point format; Scientific notation is supported; Numbers should not have leading zeroes
61	+	- "Offensive" characters in a string need to be escaped using the backslash character
62	+	- Null values are represented by the null literal in lower case
63	+	- Other object types, such as dates, are not natively supported and should be converted to strings; to be managed by the parser/client
64	+	- Each member of an object or each array value must be followed by a comma if it is not the last one
65	+	- The common extension for json files is .json
66	+	- The MIME type for json files is application/json
67	+
68	+	## Implementations
69	+
70	+	JSON implementation is not very strict, and a lot of leeway is granted to the client application and/or parser to enforce the guidelines. As usual when writing code:
71	+
72	+	- be liberal in what you accept
73	+	- be strict (adhering to the standard) in what you send.
74	+
75	+	There are two main implementations of JSON:
76	+
77	+	### The official JSON Specification syntax
78	+
79	+	This implementation adheres strictly to the RFC 4627 guidelines above and does not allow deviation from the specification.
80	+
81	+	### The Javascript syntax
82	+
83	+	This implementation follows the implementation of the Javascript programming language and as such allows for a few deviations from the official specification. For example:
84	+
85	+	1. allows un-quoted keys eg `{name: "John Doe" }`
86	+	2. allows single quotes for keys and/or string values; and a liberal mix of single and double quotes eg `{'name': "John Doe", "language":'Pascal'}`
87	+	3. allows trailing comma after the last member of an array and/or object eg `{"keywords":["if","begin","for",], "IDEs":["Lazarus","fpIDE","MSEide"],}`
88	+
89	+	## See also
90	+
91	+	- [[fcl-json]] package that implements JSON for Free Pascal and Lazarus
92	+	- [[Streaming JSON]] - (English translation from original German wiki page)
93	+
94	+	## External links
95	+
96	+	- [Official JSON website](http://www.json.org)
97	+	- [JSON Formatter](https://jsonformatter.org)
98	+
99	+	---
100	+	From the Free Pascal wiki, page "JSON", as it stood on 2021-06-08 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
101	+	Category: JSON

Back to history