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 ExampleClass : MonoBehaviour {
    void OnEnable() {
        print("script was enabled");
    }
}

Another example:

no example available in JavaScript

// Implement OnDisable and OnEnable script functions.
// These functions will be called when the attached GameObject
// is toggled.
// This example also supports the Editor.  The Update function
// will be called, for example, when the position of the
// GameObject is changed.

using UnityEngine;

[ExecuteInEditMode]
public class PrintOnOff : MonoBehaviour {

	void OnDisable() {
		Debug.Log("PrintOnDisable: script was disabled");
	}

	void OnEnable() {
		Debug.Log("PrintOnEnable: script was enabled");
	}

	void Update() { 
#if UNITY_EDITOR
		Debug.Log("Editor causes this Update"); 
#endif
	} 
}

Note: OnEnable cannot be a co-routine.
See Also: OnDisable.