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):
{
“employees”:[
{“firstName”:”Chris”, “lastName”:”Martinez”},
{“firstName”:”Joseph”, “lastName”:”Anderson”},
{“firstName”:”Ryan”, “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”:”Chris”
JSON Objects
JSON objects are written inside curly braces.
Just like in JavaScript, objects can contain multiple name/value pairs:
{“firstName”:”Chris”, “lastName”:”Martinez”}
JSON Arrays
JSON arrays are written inside square brackets.
Just like in JavaScript, an array can contain objects:
“employees”:[
{“firstName”:”Chris”, “lastName”:”Martinez”},
{“firstName”:”Joseph”, “lastName”:”Anderson”},
{“firstName”:”Ryan”, “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”:”Chris” , “lastName”:”Martinez” },’ +
‘{ “firstName”:”Joseph” , “lastName”:”Anderson” },’ +
‘{ “firstName”:”Ryan” , “lastName”:”Jones” } ]}’;
Then, use the JavaScript built-in function JSON.parse() to convert the string into a JavaScript object:
const obj = JSON.parse(text);
Example JSON data
var jsonData = ‘{“name”: “John Doe”, “age”: 30, “city”: “New York”}’;
Parsing JSON data into an object
var parsedData = JSON.parse(jsonData);
Accessing data from the parsed object
var name = parsedData.name;
var age = parsedData.age;
var city = parsedData.city;
Modifying data
parsedData.age = 31;
parsedData.city = “San Francisco”;
Converting object back to JSON
var modifiedJsonData = JSON.stringify(parsedData);
Printing the results
console.log(“Name:”, name);
console.log(“Age:”, age);
console.log(“City:”, city);
console.log(“Modified JSON Data:”, modifiedJsonData);
Note: Keep in mind that this is a simple example for understanding the basic concepts of working with JSON in JavaScript. In real-world scenarios, you may need to handle more complex JSON structures and handle errors during parsing or stringifying JSON data.