Tutorials References Menu

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Statements JS Syntax JS Comments JS Variables JS Let JS Const JS Operators JS Arithmetic JS Assignment JS Data Types JS Functions JS Objects JS Events JS Strings JS String Methods JS String Search JS Numbers JS Number Methods JS Arrays JS Array Methods JS Array Sort JS Array Iteration JS Array Const JS Dates JS Date Formats JS Date Get Methods JS Date Set Methods JS Math JS Random JS Booleans JS Comparisons JS Conditions JS Switch JS Loop For JS Loop For In JS Loop For Of JS Loop While JS Break JS Typeof JS Type Conversion JS Bitwise JS RegExp JS Errors JS Scope JS Hoisting JS Strict Mode JS this Keyword JS Arrow Function JS Classes JS JSON JS Debugging JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words

JS Objects

Object Definitions Object Properties Object Methods Object Display Object Accessors Object Constructors Object Prototypes Object Reference Object Map() Object Set()

JS Functions

Function Definitions Function Parameters Function Invocation Function Call Function Apply Function Closures

JS Classes

Class Intro Class Inheritance Class Static

JS Async

JS Callbacks JS Asynchronous JS Promises JS Async/Await

JS Versions

JS Versions JS 2009 (ES5) JS 2015 (ES6) JS 2016 JS 2017 JS 2018 JS IE / Edge JS History

JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM Forms DOM CSS DOM Animations DOM Events DOM Event Listener DOM Navigation DOM Nodes DOM Collections DOM Node Lists

JS Browser BOM

JS Window JS Screen JS Location JS History JS Navigator JS Popup Alert JS Timing JS Cookies

JS Web APIs

Web API Intro Web Forms API Web History API Web Storage API Web Worker API Web Fetch API Web Geolocation API

JS AJAX

AJAX Intro AJAX XMLHttp AJAX Request AJAX Response AJAX XML File AJAX PHP AJAX ASP AJAX Database AJAX Applications AJAX Examples

JS JSON

JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Parse JSON Stringify JSON Objects JSON Arrays JSON Server JSON PHP JSON HTML JSON JSONP

JS vs jQuery

jQuery Selectors jQuery HTML jQuery CSS jQuery DOM

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Editor

JS References

JavaScript Objects HTML DOM Objects


JSON Syntax


The JSON syntax is a subset of the JavaScript syntax.


JSON Syntax Rules

JSON syntax is derived from JavaScript object notation syntax:

  • 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 (aka key/value pairs).

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

Example

"name":"John"

JSON names require double quotes.


JSON - Evaluates to JavaScript Objects

The JSON format is almost identical to JavaScript objects.

In JSON, keys must be strings, written with double quotes:

JSON

{"name":"John"}

In JavaScript, keys can be strings, numbers, or identifier names:

JavaScript

{name:"John"}


JSON Values

In JSON, values must be one of the following data types:

  • a string
  • a number
  • an object
  • an array
  • a boolean
  • null

In JavaScript values can be all of the above, plus any other valid JavaScript expression, including:

  • a function
  • a date
  • undefined

In JSON, string values must be written with double quotes:

JSON

{"name":"John"}

In JavaScript, you can write string values with double or single quotes:

JavaScript

{name:'John'}

JavaScript Objects

Because JSON syntax is derived from JavaScript object notation, very little extra software is needed to work with JSON within JavaScript.

With JavaScript you can create an object and assign data to it, like this:

Example

person = {name:"John", age:31, city:"New York"};

You can access a JavaScript object like this:

Example

// returns John
person.name;
Try it Yourself »

It can also be accessed like this:

Example

// returns John
person["name"];
Try it Yourself »

Data can be modified like this:

Example

person.name = "Gilbert";
Try it Yourself »

It can also be modified like this:

Example

person["name"] = "Gilbert";
Try it Yourself »

You will learn how to convert JavaScript objects into JSON later in this tutorial.


JavaScript Arrays as JSON

The same way JavaScript objects can be written as JSON, JavaScript arrays can also be written as JSON.

You will learn more about objects and arrays later in this tutorial.


JSON Files

  • The file type for JSON files is ".json"
  • The MIME type for JSON text is "application/json"