Encode

Turn a php array into a JSON string.

$assoc = array('a' => 1, 'b' => 2, 'c' => 3);
echo json_encode($assoc);
// '{"a":1,"b":2,"c":3}'

$array = array('a', 'b', 'c');
echo json_encode($array);
// '["a","b","c"]'

$array = array('a', 'b', 'c');
echo json_encode($array, JSON_FORCE_OBJECT);
// '{"0":"a","1":"b","2":"c"}'

Decode

Turn a JSON string into a native php array.

JSON Array

$json = '["apple","orange","banana","strawberry"]';
$ar = json_decode($json);
echo $ar[0]; // apple

JSON Object

$json = '{
    "title": "JavaScript: The Definitive Guide",
    "author": "David Flanagan"
}';
$book = json_decode($json);
echo $book->title; // JavaScript: The Definitive Guide 
//or
$book = json_decode($json, true);
echo $book['title']; // JavaScript: The Definitive Guide

JSON Complex Data

$json = '[
    {
        "title": "Professional JavaScript",
        "author": "Nicholas C. Zakas"
    },
    {
        "title": "JavaScript: The Definitive Guide",
        "author": "David Flanagan"
    }
]';

$books = json_decode($json);
echo $books[1]->title; // JavaScript: The Definitive Guide
//or
$books = json_decode($json, true);
echo $books[1]['title']; // JavaScript: The Definitive Guide

More Info: http://www.dyn-web.com/tutorials/php-js/json/decode.php

Detect if AJAX Request

function is_ajax_request() {
    return isset($_SERVER['HTTP_X_REQUESTED_WITH']) && $_SERVER['HTTP_X_REQUESTED_WITH'] == 'XMLHttpRequest';
}
if(is_ajax_request()) {
    echo "Ajax response";
} else {
    echo "Not ajax";
}