Alert when no layers are selected.

[threedeeNYC]

Hello,
I want an alert prompt if there are no layers selected. 
I have this to set up my variables.

//set variables
myProj = app.project;
myComp = myProj.activeItem;
myLayer = myComp.selectedLayers[0];

//my code

if (myLayer === undefined){
alert ("Select a Layer);
}

Ive tried myLayer == 0, and myLayer == null;

Any help is appreciated. Thanks!

[threedeeNYC]

i have end quotes on the alert above. Just a typo here 

[Mylenium]

Layer selections are arrays. You have to query the size of the array with myLayers.length, not the contents of the collection.

Mylenium

[Mathias Moehl]

var myProj = app.project;
var myComp = myProj.activeItem;
if(!(myComp instaneof CompItem)) alert("please select a layer (active item is not a composition)");
else {

    if(myComp.selectedLayers.length ==0) alert("please select a layer (a comp is active, but there is no layer selected in this active comp)");

}

(I didn't check the code, it might contain typos)