Powershell: importing module

How do I usually import an AD powershell module? I think the same way as you do:

Import-Module -Name ActiveDirectory -ErrorAction SilentlyContinue

How do I import another one in a script body a slightly wiser way using a custom function to determine if module exists in a system or is already loaded?

Function ImportModule($modulename) {
 if(-not(Get-Module $modulename)) {
 if(Get-Module -ListAvailable | Where-Object { $_.name -eq $modulename }) {
 Import-Module -Name $modulename
 } else {
 "Module $modulename not found. Exiting.";Exit
 }
 } else {
 "Module $modulename already loaded"
 }
 }
 ImportModule ActiveDirectory