This function can be used to check if the given layer exists. You supply the layer ID (which you get when you create the layer using layer_create()) or the layer name (as a string - this will have a performance impact) and the function will return a boolean value of true if it exists or false if it does not.NOTE: This function works within the scope of the current target room - by default the room in which the function is called - which can be set using the function layer_set_target_room().
Argument Description layer_name The name of the layer (a string or ID value)
global.tileLayer = layer_create(1000);
The above code will check to see if the layer stored in the global variable actually exists, and if it does not then it is created.