Using json and javascript

JSON

The JSON namespace object contains static methods for parsing values from and converting values to JavaScript Object Notation (JSON).

Description

Unlike most global objects, JSON is not a constructor. You cannot use it with the new operator or invoke the JSON object as a function. All properties and methods of JSON are static (just like the Math object).

JavaScript and JSON differences

JSON is a syntax for serializing objects, arrays, numbers, strings, booleans, and null . It is based upon JavaScript syntax, but is distinct from JavaScript: most of JavaScript is not JSON. For example:

Property names must be double-quoted strings; trailing commas are forbidden.

Leading zeros are prohibited. A decimal point must be followed by at least one digit. NaN and Infinity are unsupported.

Any JSON text is a valid JavaScript expression, but only after the JSON superset revision. Before the revision, U+2028 LINE SEPARATOR and U+2029 PARAGRAPH SEPARATOR are allowed in string literals and property keys in JSON; but the same use in JavaScript string literals is a SyntaxError .

Other differences include allowing only double-quoted strings and no support for undefined or comments. For those who wish to use a more human-friendly configuration format based on JSON, there is JSON5, used by the Babel compiler, and the more commonly used YAML.

The same text may represent different values in JavaScript object literals vs. JSON as well. For more information, see Object literal syntax vs. JSON.

Full JSON grammar

Valid JSON syntax is formally defined by the following grammar, expressed in ABNF, and copied from IETF JSON standard (RFC):

JSON-text = object / array begin-array = ws %x5B ws ; [ left square bracket begin-object = ws %x7B ws ; < left curly bracket end-array = ws %x5D ws ; ] right square bracket end-object = ws %x7D ws ; >right curly bracket name-separator = ws %x3A ws ; : colon value-separator = ws %x2C ws ; , comma ws = *( %x20 / ; Space %x09 / ; Horizontal tab %x0A / ; Line feed or New line %x0D ; Carriage return ) value = false / null / true / object / array / number / string false = %x66.61.6c.73.65 ; false null = %x6e.75.6c.6c ; null true = %x74.72.75.65 ; true object = begin-object [ member *( value-separator member ) ] end-object member = string name-separator value array = begin-array [ value *( value-separator value ) ] end-array number = [ minus ] int [ frac ] [ exp ] decimal-point = %x2E ; . digit1-9 = %x31-39 ; 1-9 e = %x65 / %x45 ; e E exp = e [ minus / plus ] 1*DIGIT frac = decimal-point 1*DIGIT int = zero / ( digit1-9 *DIGIT ) minus = %x2D ; - plus = %x2B ; + zero = %x30 ; 0 string = quotation-mark *char quotation-mark char = unescaped / escape ( %x22 / ; " quotation mark U+0022 %x5C / ; \ reverse solidus U+005C %x2F / ; / solidus U+002F %x62 / ; b backspace U+0008 %x66 / ; f form feed U+000C %x6E / ; n line feed U+000A %x72 / ; r carriage return U+000D %x74 / ; t tab U+0009 %x75 4HEXDIG ) ; uXXXX U+XXXX escape = %x5C ; \ quotation-mark = %x22 ; " unescaped = %x20-21 / %x23-5B / %x5D-10FFFF HEXDIG = DIGIT / %x41-46 / %x61-66 ; 0-9, A-F, or a-f ; HEXDIG equivalent to HEXDIG rule in [RFC5234] DIGIT = %x30-39 ; 0-9 ; DIGIT equivalent to DIGIT rule in [RFC5234]

Insignificant whitespace may be present anywhere except within a JSONNumber (numbers must contain no whitespace) or JSONString (where it is interpreted as the corresponding character in the string, or would cause an error). The tab character (U+0009), carriage return (U+000D), line feed (U+000A), and space (U+0020) characters are the only valid whitespace characters.

Static properties

The initial value of the @@toStringTag property is the string «JSON» . This property is used in Object.prototype.toString() .

Static methods

Parse a piece of string text as JSON, optionally transforming the produced value and its properties, and return the value.

Return a JSON string corresponding to the specified value, optionally including only certain properties or replacing property values in a user-defined manner.

Examples

Example JSON

 "browsers":  "firefox":  "name": "Firefox", "pref_url": "about:config", "releases":  "1":  "release_date": "2004-11-09", "status": "retired", "engine": "Gecko", "engine_version": "1.7" > > > > > 

You can use the JSON.parse() method to convert the above JSON string into a JavaScript object:

const jsonText = ` < "browsers": < "firefox": < "name": "Firefox", "pref_url": "about:config", "releases": < "1": < "release_date": "2004-11-09", "status": "retired", "engine": "Gecko", "engine_version": "1.7" >> > > >`; console.log(JSON.parse(jsonText)); 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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JavaScript JSON

JSON is often used when data is sent from a server to a web page.

What is JSON?

• JSON stands for JavaScript Object Notation
• JSON is a lightweight data interchange format
• JSON is language independent *
• JSON is «self-describing» and easy to understand

* The JSON syntax is derived from JavaScript object notation syntax, but the JSON format is text only. Code for reading and generating JSON data can be written in any programming language.

JSON Example

This JSON syntax defines an employees object: an array of 3 employee records (objects):

JSON Example

The JSON Format Evaluates to JavaScript Objects

The JSON format is syntactically identical to the code for creating JavaScript objects.

Because of this similarity, a JavaScript program can easily convert JSON data into native JavaScript objects.

JSON Syntax Rules

• Data is in name/value pairs
• Data is separated by commas
• Curly braces hold objects
• Square brackets hold arrays

JSON Data — A Name and a Value

JSON data is written as name/value pairs, just like JavaScript object properties.

A name/value pair consists of a field name (in double quotes), followed by a colon, followed by a value:

JSON names require double quotes. JavaScript names do not.

JSON Objects

JSON objects are written inside curly braces.

Just like in JavaScript, objects can contain multiple name/value pairs:

JSON Arrays

JSON arrays are written inside square brackets.

Just like in JavaScript, an array can contain objects:

In the example above, the object «employees» is an array. It contains three objects.

Each object is a record of a person (with a first name and a last name).

Converting a JSON Text to a JavaScript Object

A common use of JSON is to read data from a web server, and display the data in a web page.

For simplicity, this can be demonstrated using a string as input.

First, create a JavaScript string containing JSON syntax:

Then, use the JavaScript built-in function JSON.parse() to convert the string into a JavaScript object:

Finally, use the new JavaScript object in your page:

Example

document.getElementById(«demo»).innerHTML =
obj.employees[1].firstName + » » + obj.employees[1].lastName;

You can read more about JSON in our JSON tutorial.

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