computer science

JSON

JSON is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand JSON rather than just read about it. In short: JSON (JavaScript Object Notation, pronounced or ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of name–value pairs and arrays (or other serializable values). It is a commonly used data format with diverse uses in electronic data interchange, including that of web applications with servers.

Key takeaways

JSON belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect JSON to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of JSON from memory before moving on to harder problems.

Reference excerpt

JSON (JavaScript Object Notation, pronounced or ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of name–value pairs and arrays (or other serializable values). It is a commonly used data format with diverse uses in electronic data interchange, including that of web applications with servers. JSON is a programming language-independent data format. It was derived from JavaScript, but many modern programming languages include code to generate and parse JSON-format data. JSON filenames use the extension .json. Douglas Crockford originally specified the JSON format in the early 2000s. He and Chip Morningstar sent the first JSON message in April 2001.

Naming and pronunciation The 2017 international standard (ECMA-404 and ISO/IEC 21778:2017) specifies that "JSON" is "pronounced , as in 'Jason and The Argonauts'". The first (2013) edition of ECMA-404 did not address the pronunciation. Crockford said in 2011, "There's a lot of argument about how you pronounce that, but I strictly don't care." is another common pronunciation.

Standards After RFC 4627 had been available as its "informational" specification since 2006, JSON was first standardized in 2013, as ECMA-404. RFC 8259, published in 2017, is the current version of the Internet Standard STD 90, and it remains consistent with ECMA-404. That same year, JSON was also standardized as ISO/IEC 21778:2017. The ECMA and ISO/IEC standards describe only the allowed syntax, whereas the RFC covers some security and interoperability considerations.

History

JSON grew out of a need for a real-time server-to-browser session communication protocol without using browser plugins such as Flash or Java applets, the dominant methods used in the early 2000s. Crockford first specified and popularized the JSON format. The acronym originated at State Software, a company cofounded by Crockford and others in March 2001. The cofounders agreed to build a system that used standard browser capabilities and provided an abstraction layer for Web developers to create stateful Web applications that had a persistent duplex connection to a Web server by holding two Hypertext Transfer Protocol (HTTP) connections open and recycling them before standard browser time-outs if no further data were exchanged. The cofounders had a round-table discussion and voted on whether to call the data format JSML (JavaScript Markup Language) or JSON (JavaScript Object Notation), as well as under what license type to make it available. The JSON.org website was launched in 2001. In December 2005, Yahoo! began offering some of its Web services in JSON. A precursor to the JSON libraries was used in a children's digital asset trading game project named Cartoon Orbit at Communities.com which used a browser side plug-in with a proprietary messaging format to manipulate DHTML elements. Upon discovery of early Ajax capabilities, digiGroups, Noosh, and others used frames to pass information into the user browsers' visual field without refreshing a Web application's visual context, realizing real-time rich Web applications using only the standard HTTP, HTML, and JavaScript capabilities of Netscape 4.0.5+ and Internet Explorer 5+. Crockford then found that JavaScript could be used as an object-based messaging format for such a system. The system was sold to Sun Microsystems, Amazon.com, and EDS. JSON was based on a subset of the JavaScript scripting language (specifically, Standard ECMA-262 3rd Edition—December 1999) and is commonly used with JavaScript, but it is a language-independent data format. Code for parsing and generating JSON data is readily available in many programming languages. JSON's website lists JSON libraries by language. In October 2013, Ecma International published the first edition of its JSON standard ECMA-404. That same year, RFC 7158 used ECMA-404 as a reference. In 2014, RFC 7159 became the main reference for JSON's Internet uses, superseding RFC 4627 and RFC 7158 (but preserving ECMA-262 and ECMA-404 as main references). In November 2017, ISO/IEC JTC 1/SC 22 published ISO/IEC 21778:2017 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. 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.

Syntax The following example shows a possible JSON representation describing a person.

Character encoding Although Crockford originally asserted that JSON is a strict subset of JavaScript and ECMAScript, 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. 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. 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:

Or:

JSON became a strict subset of ECMAScript as of the language's 2019 revision.

Data types JSON's basic data types are:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with JSON

Start with the simplest possible case. Write down what JSON claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to JSON before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about JSON ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of JSON

In research: JSON appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses JSON in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: JSON is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ajax (programming), Computer-related introductions in 2001, Ecma standards, so understanding it makes those chapters shorter.
In everyday life: Look for JSON outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study JSON in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what JSON means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain JSON out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is JSON in simple terms?

Why does JSON matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study JSON?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on JSON.