function_exists
PHP 4, PHP 5, PHP 7, PHP 8
function_exists - Return true if the given function has been defined
Manual
function_exists(
string$function ): bool
Checks the list of defined functions, both built-in (internal) and user-defined, for function.
Parameters
- function
-
The function name, as a string.
Return Values
Returns true if function exists and is a function, false otherwise.
Note:
This function will return false for constructs, such as include_once and echo.
Notes
Note:
A function name may exist even if the function itself is unusable due to configuration or compiling options (with the image functions being an example).