Need workaround for this line of code

Been trying to use/convert an old C# script on youtube tutorial into javascript for use in my project. All was going well until I hit this line of code -

 CurrentlySelectedUnit.transform.FindChild("Selected").gameObject.active = false;
 
 CurrentlySelectedUnit = null;
 

Which gave me this error -

"Assets/Scripts/MousePoint 2.js(24,82): BCW0012: WARNING: 'UnityEngine.GameObject.active' is obsolete. GameObject.active is obsolete. Use GameObject.SetActive(), GameObject.activeSelf or GameObject.activeInHierarchy.

if I use 'GameObject.SetActive' I get this error -

"Assets/Scripts/MousePoint 2.js(24,71): BCE0019: 'GameObject' is not a member of 'UnityEngine.Transform'. "

If I use 'GameObject.activeSelf' I get the same error -

"Assets/Scripts/MousePoint 2.js(24,71): BCE0019: 'GameObject' is not a member of 'UnityEngine.Transform'. "

And if I use 'GameObject.activeInHierarchy' I get the same again.

How can I fix this as the only solutions it gives me, causes more errors ???