This should work:
var documentsArray = app.documents.everyItem().getElements();for (var i = 0; i < documentsArray.length; i++) { var document = documentsArray[i]; var layers = document.layers; layers.itemByName("Interactive - Web").visible = true; layers.itemByName("Interactive - Print").visible = false;}
Also, it might be possible to do this without using "getElements" which "resolves the object specifier", eliminating the need for the "for" loop. Something like this:
app.documents.everyItem().layers.itemByName("Interactive - Web").visible = true;
app.documents.everyItem().layers.itemByName("Interactive - Print").visible = false;