Find If PHP Extension is Loaded

Use extension_loaded() to test whether a given extension is already available or not. This works on both built-in extensions and dynamically loaded ones.
http://php.net/manual/en/function.extension-loaded.php

List of Loaded Extensions

print_r(get_loaded_extensions());

Function to Check if an extension id loaded

function is_loaded ($php_extension) {
	if (!extension_loaded($php_extension)) {
		echo $php_extension. ' is NOT loaded';
	}
	else {
		echo $php_extension. ' is loaded';
	}
}
is_loaded ('gd');