JavaScript JSON

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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.













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Reference: https://www.w3schools.com/js/js_json.asp