MonoBehaviour.OnEnable()
Description

This function is called when the object becomes enabled and active.

	function OnEnable () {
		print("script was enabled");
	}
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnEnable() {
        print("script was enabled");
    }
}
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnEnable() as void:
		print('script was enabled')

OnEnable cannot be a co-routine.