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JSON Syntax

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JSON syntax is a subset of JavaScript syntax

JSON Syntax Rules

JSON syntax is a subset of the JavaScript object notation syntax.

Data is in name/value pairs
Data is separated by comma
Curly brackets holds objects
Square brackets holds arrays

JSON Name/Value Pairs

JSON data is written as name/value pairs.

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

"firstName" : "John"

This is simple to understand, and equals to the JavaScript statement:

firstName = "John"

JSON Values

JSON values can be:

A number (integer or floating point)
A string (in double quotes)
A Boolean (true or false)
An array (in square brackets)
An object (in curly brackets)
null

JSON Objects

JSON objects are written inside curly brackets,

Objects can contain multiple name/values pairs:

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

This is also simple to understand, and equals to the JavaScript statements:

firstName = "John"
lastName = "Doe"

JSON Arrays

JSON arrays are written inside square brackets.

An array can contain multiple objects:

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

In the example above, the object "employees" is an array containing three objects. Each object is a record of a person (with a first name and a last name).

JSON Uses JavaScript Syntax

Because JSON uses JavaScript syntax, no extra software is needed to work with JSON within JavaScript.

With JavaScript you can create an array of objects and assign data to it like this:

Example

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

The first entry in the JavaScript object array can be accessed like this:

employees[0].lastName;

The returned content will be:

Doe

The data can be modified like this:

employees[0].lastName = "Jonatan";

Try it yourself »

In the next chapter you will learn how to convert a JSON text to a JavaScript object.

JSON Files

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