Javascript To Enable Or Disable Controls In ASP Forms

I am trying to write javascript which will enable or disable a control on client side. I am writing a sample code here in VB but it will not work on client side, I need same kind of code in Java:

Function SetControl(ByVal ControlName As Control, ByVal strAction As integer)
If strAction = 0 Then
ControlName.Enabled = True
Else
ControlName.Enabled = False
End If
End Function

this code will not work, it is just an example and I need this kind of script to place on the top of my page which I can use on client side.