has_filter()

has_filter() — Checks if any filter has been registered for a hook. When using the $callback argument, this function may return a non-boolean value that evaluates to false (e.g. 0), so use the === operator for testing the return value.

Inputs: $hook_name (string): The name of the filter hook. $callback (callable|string|array|false): Optional. The callback to check for. This function can be called unconditionally to speculatively check a callback that may or may not exist. Default false. $priority (int|false): Optional. The specific priority at which to check for the callback. Default false.

Returns bool|int: If $callback is omitted, returns boolean for whether the hook has anything registered. When checking a specific function, the priority of that hook is returned, or false if the function is not attached. If $callback and $priority are both provided, a boolean is returned for whether the specific function is registered at that priority.