Tutorials References Exercises VideosMenu
Free WebsiteGet CertifiedPro

JS Tutorial

JS HOMEJS IntroductionJS Where ToJS OutputJS StatementsJS SyntaxJS CommentsJS VariablesJS LetJS ConstJS OperatorsJS ArithmeticJS AssignmentJS PrecedenceJS Data TypesJS FunctionsJS ObjectsJS EventsJS StringsJS String MethodsJS String SearchJS String TemplatesJS NumbersJS Number MethodsJS ArraysJS Array MethodsJS Array SortJS Array IterationJS Array ConstJS DatesJS Date FormatsJS Date Get MethodsJS Date Set MethodsJS MathJS RandomJS BooleansJS ComparisonsJS If ElseJS SwitchJS Loop ForJS Loop For InJS Loop For OfJS Loop WhileJS BreakJS IterablesJS SetsJS MapsJS TypeofJS Type ConversionJS BitwiseJS RegExpJS ErrorsJS ScopeJS HoistingJS Strict ModeJS this KeywordJS Arrow FunctionJS ClassesJS ModulesJS JSONJS DebuggingJS Style GuideJS Best PracticesJS MistakesJS PerformanceJS Reserved Words

JS Versions

JS VersionsJS 2009 (ES5)JS 2015 (ES6)JS 2016JS 2017JS 2018JS 2019JS 2020JS IE / EdgeJS History

JS Objects

Object DefinitionsObject PropertiesObject MethodsObject DisplayObject AccessorsObject ConstructorsObject PrototypesObject IterablesObject SetsObject MapsObject Reference

JS Functions

Function DefinitionsFunction ParametersFunction InvocationFunction CallFunction ApplyFunction BindFunction Closures

JS Classes

Class IntroClass InheritanceClass Static

JS Async

JS CallbacksJS AsynchronousJS PromisesJS Async/Await

JS HTML DOM

DOM IntroDOM MethodsDOM DocumentDOM ElementsDOM HTMLDOM FormsDOM CSSDOM AnimationsDOM EventsDOM Event ListenerDOM NavigationDOM NodesDOM CollectionsDOM Node Lists

JS Browser BOM

JS WindowJS ScreenJS LocationJS HistoryJS NavigatorJS Popup AlertJS TimingJS Cookies

JS Web APIs

Web API IntroWeb Forms APIWeb History APIWeb Storage APIWeb Worker APIWeb Fetch APIWeb Geolocation API

JS AJAX

AJAX IntroAJAX XMLHttpAJAX RequestAJAX ResponseAJAX XML FileAJAX PHPAJAX ASPAJAX DatabaseAJAX ApplicationsAJAX Examples

JS JSON

JSON IntroJSON SyntaxJSON vs XMLJSON Data TypesJSON ParseJSON StringifyJSON ObjectsJSON ArraysJSON ServerJSON PHPJSON HTMLJSON JSONP

JS vs jQuery

jQuery SelectorsjQuery HTMLjQuery CSSjQuery DOM

JS Graphics

JS GraphicsJS CanvasJS PlotlyJS Chart.jsJS Google ChartJS D3.js

JS Examples

JS ExamplesJS HTML DOMJS HTML InputJS HTML ObjectsJS HTML EventsJS BrowserJS EditorJS ExercisesJS QuizJS Certificate

JS References

JavaScript ObjectsHTML DOM Objects


JavaScript JSON


JSON is a format for storing and transporting data.

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

{
"employees":[
  {"firstName":"John", "lastName":"Doe"},
  {"firstName":"Anna", "lastName":"Smith"},
  {"firstName":"Peter", "lastName":"Jones"}
]
}

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:

"firstName":"John"

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:

{"firstName":"John", "lastName":"Doe"}

JSON Arrays

JSON arrays are written inside square brackets.

Just like in JavaScript, an array can contain objects:

"employees":[
  {"firstName":"John", "lastName":"Doe"},
  {"firstName":"Anna", "lastName":"Smith"},
  {"firstName":"Peter", "lastName":"Jones"}
]

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:

let text ='{ "employees" : [' +
'{ "firstName":"John" , "lastName":"Doe" },' +
'{ "firstName":"Anna" , "lastName":"Smith" },' +
'{ "firstName":"Peter" , "lastName":"Jones" } ]}';

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

const obj = JSON.parse(text);

Finally, use the new JavaScript object in your page:

Example

<p id="demo"></p>

<script>
document.getElementById("demo").innerHTML =
obj.employees[1].firstName + " " + obj.employees[1].lastName;
</script>
Try it Yourself »

You can read more about JSON in our JSON tutorial.