fix multiple screen finding. throw errors on edge cases.

lib/widgets/node.js

@@ -15,6 +15,7 @@ var EventEmitter = require('../events').EventEmitter;
  */
 
 function Node(options) {
+  var self = this;
   var Screen = require('./screen');
 
   if (!(this instanceof Node)) {
@@ -38,9 +39,20 @@ function Node(options) {
       while (this.screen && this.screen.type !== 'screen') {
         this.screen = this.screen.parent;
       }
-    } else if (Screen.global) {
-      // Should never happen:
-      this.screen = Screen.global;
+    } else if (Screen.total) {
+      // This _should_ work in most cases as long as the element is appended
+      // synchronously after the screen's creation. Throw error if not.
+      this.screen = Screen.instances[Screen.instances.length - 1];
+      process.nextTick(function() {
+        if (!self.parent) {
+          throw new Error('Element (' + self.type + ')'
+            + ' was not appended synchronously after the'
+            + ' screen\'s creation. Please set a `parent`'
+            + ' or `screen` option in the element\'s constructor'
+            + ' if you are going to use multiple screens and'
+            + ' append the element later.');
+        }
+      });
     } else {
       throw new Error('No active screen.');
     }
@@ -72,6 +84,10 @@ Node.prototype.type = 'node';
 Node.prototype.insert = function(element, i) {
   var self = this;
 
+  if (element.screen && element.screen !== this.screen) {
+    throw new Error('Cannot switch a node\'s screen.');
+  }
+
   element.detach();
   element.parent = this;
   element.screen = this.screen;