What are common mistakes when decoding JSON in PHP?

Common mistakes when decoding JSON in PHP include not checking if the JSON string is valid before decoding it, not handling errors that may occur during decoding, and not using the appropriate decoding function based on the JSON data structure. To avoid these mistakes, you can first validate the JSON string using `json_last_error()` function, handle any errors using `json_last_error_msg()` function, and use either `json_decode()` or `json_decode()` with the second parameter set to `true` for associative arrays.

$jsonString = '{"key": "value"}';

// Validate JSON string
if (json_last_error() !== JSON_ERROR_NONE) {
    echo 'Invalid JSON: ' . json_last_error_msg();
    exit;
}

// Decode JSON string
$data = json_decode($jsonString, true);

if ($data === null) {
    echo 'Error decoding JSON: ' . json_last_error_msg();
    exit;
}

// Access decoded data
echo $data['key'];