What Is JSON?

JSON (JavaScript Object Notation) is a plain-text format for sending and storing data. Despite the name, nearly every programming language can read and write it, and almost every web API uses it.

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{
    "name": "Isha",
    "age": 29,
    "active": true,
    "skills": ["php", "sql"],
    "address": {
        "city": "Pune",
        "postcode": "411001"
    },
    "manager": null
}

Why JSON matters in PHP

• A JavaScript front end asks your PHP code for data, and you answer in JSON.
• A mobile app talks to your server with JSON.
• You call other services (payments, maps, weather) and read their JSON replies.
• You store settings or flexible data in a JSON file or column.

The syntax

JSON has only a few building blocks.

The rules (stricter than PHP)

• Strings use double quotes only. 'single' is invalid.
• Keys must be strings in double quotes.
• No trailing commas, no comments.
• No undefined, no functions, no dates (dates are written as strings).

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<?php
var_dump(json_decode('{"name": "Ana"}', true));
var_dump(json_decode("{'name': 'Ana'}", true));   // single quotes: invalid

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array(1) {
  ["name"]=>
  string(3) "Ana"
}
NULL

Reading and writing it

PHP has two main functions, covered in the next lessons.

• json_encode() turns a PHP value into a JSON string.
• json_decode() turns a JSON string into a PHP value.

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<?php
$data = ["name" => "Ana", "skills" => ["php", "sql"]];

$json = json_encode($data);

echo $json . "\n";

$back = json_decode($json, true);

echo $back["skills"][1];

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{"name":"Ana","skills":["php","sql"]}
sql

JSON vs XML vs CSV

MIME type

When a server sends JSON, it sets the header Content-Type: application/json. See Building a JSON Response.

Pretty or compact

Both of these are the same data. APIs usually send the compact form to save bytes. A pretty form is for people.