Redesign DOMList and review its implementations.

DOMList is now no more than an interface for things that have a
`length` and index properties. We add a Seq view of all DOMLists
in its companion object. We make it read-only and covariant, as
its implementations are actually not mutable in the DOM standard.

We review all its subclasses and subtraits:

* Make them classes iff they are exposed and can be used with
  `instanceof`. Their constructors are always private. Otherwise,
  make them traits.
* Explicitly declare `item()` iff it is supported in the given
  class/trait (it used to be in `DOMList`, but not all
  implementations support `item()`).

We make `NodeList` parameterized and covariant in the type of node.
We deprecate `NodeListOf` in favor of `NodeList`.

Author: sjrd

src/main/scala/org/scalajs/dom/CSSTypes.scala

@@ -479,7 +479,9 @@ class CSSPageRule extends CSSRule {
  */
 @js.native
 @JSGlobal
-class CSSRuleList extends DOMList[CSSRule]
+class CSSRuleList private[this] () extends DOMList[CSSRule] {
+  def item(index: Int): CSSRule = js.native
+}
 
 /**
  * The CSSKeyframesRule interface describes an object representing a complete set

src/main/scala/org/scalajs/dom/HTMLTypes.scala

@@ -1157,7 +1157,8 @@ abstract class HTMLMenuElement extends HTMLElement {
  */
 @js.native
 @JSGlobal
-abstract class HTMLCollection extends DOMList[Element] {
+class HTMLCollection private[this] () extends DOMList[Element] {
+  def item(index: Int): Element = js.native
 
   /**
    * Returns the specific node whose ID or, as a fallback, name matches the string

src/main/scala/org/scalajs/dom/SVGTypes.scala

@@ -1244,7 +1244,7 @@ abstract class SVGSVGElement
    * MDN
    */
   def getIntersectionList(rect: SVGRect,
-      referenceElement: SVGElement): NodeList = js.native
+      referenceElement: SVGElement): NodeList[Node] = js.native
 
   /**
    * Unsuspends (i.e., unpauses) currently running animations that are defined
@@ -1327,7 +1327,7 @@ abstract class SVGSVGElement
   def createSVGAngle(): SVGAngle = js.native
 
   def getEnclosureList(rect: SVGRect,
-      referenceElement: SVGElement): NodeList = js.native
+      referenceElement: SVGElement): NodeList[Node] = js.native
 
   /**
    * Creates an SVGTransform object outside of any document trees. The object is

src/main/scala/org/scalajs/dom/ext/Extensions.scala

@@ -12,30 +12,6 @@ import scala.scalajs.js.typedarray.TypedArrayBufferOps._
 import org.scalajs.dom
 import org.scalajs.dom.{Blob, FormData, KeyboardEvent}
 
-/**
- * Used to extend out javascript *Collections to make them usable as normal
- * Scala Seq[*]s
- */
-class EasySeq[T](jsLength: Int, jsApply: Int => T)
-    extends scala.collection.Seq[T] {
-
-  def length = jsLength
-
-  def apply(x: Int) = jsApply(x)
-
-  def iterator = new Iterator[T] {
-    var index = 0
-
-    def hasNext: scala.Boolean = index < jsLength
-
-    def next() = {
-      val res = jsApply(index)
-      index += 1
-      res
-    }
-  }
-}
-
 /**
  * A list of the codes returned by KeyEvents.
  */

src/main/scala/org/scalajs/dom/ext/package.scala

@@ -518,7 +518,7 @@ trait NodeSelector extends js.Object {
    *
    * MDN
    */
-  def querySelectorAll(selectors: String): NodeList = js.native
+  def querySelectorAll(selectors: String): NodeList[Node] = js.native
 
   /**
    * Returns the first element within the document (using depth-first pre-order
@@ -1134,7 +1134,7 @@ abstract class Node extends EventTarget {
    *
    * MDN
    */
-  def childNodes: NodeList = js.native
+  def childNodes: NodeList[Node] = js.native
 
   /**
    * Returns a DOMString containing the name of the Node. The structure of the name will
@@ -2977,8 +2977,9 @@ class TouchEvent(typeArg: String, init: js.UndefOr[TouchEventInit])
  * MDN
  */
 @js.native
-@JSGlobal
-class TouchList extends DOMList[Touch]
+trait TouchList extends DOMList[Touch] {
+  def item(index: Int): Touch = js.native
+}
 
 /**
  * A Touch object represents a single point of contact between the user and a touch-sensitive
@@ -3337,7 +3338,7 @@ abstract class Document
    *
    * MDN
    */
-  def getElementsByName(elementName: String): NodeList = js.native
+  def getElementsByName(elementName: String): NodeList[Node] = js.native
 
   /**
    * Returns a HTMLCollection of elements with the given tag name. The complete
@@ -5014,14 +5015,14 @@ trait MutationRecord extends js.Object {
    *
    * MDN
    */
-  def addedNodes: NodeList = js.native
+  def addedNodes: NodeList[Node] = js.native
 
   /**
    * Return the nodes removed. Will be an empty NodeList if no nodes were removed.
    *
    * MDN
    */
-  def removedNodes: NodeList = js.native
+  def removedNodes: NodeList[Node] = js.native
 
   /**
    * Return the previous sibling of the added or removed nodes, or null.
@@ -6290,14 +6291,40 @@ class StyleSheet extends js.Object {
 }
 
 @js.native
-trait DOMList[T] extends js.Object {
+trait DOMList[+T] extends js.Object {
   def length: Int = js.native
-  def item(index: Int): T = js.native
-  @scala.scalajs.js.annotation.JSBracketAccess
+
+  @JSBracketAccess
   def apply(index: Int): T = js.native
+}
 
-  @scala.scalajs.js.annotation.JSBracketAccess
-  def update(index: Int, v: T): Unit = js.native
+object DOMList {
+  implicit def domListAsSeq[T](domList: DOMList[T]): scala.collection.Seq[T] =
+    new DOMListSeq(domList)
+
+  private final class DOMListSeq[+T](domList: DOMList[T])
+      extends scala.collection.Seq[T] {
+
+    def length: Int = domList.length
+
+    def apply(x: Int): T = domList(x)
+
+    def iterator: Iterator[T] = new DOMListIterator(domList)
+  }
+
+  private final class DOMListIterator[+T](domList: DOMList[T])
+      extends Iterator[T] {
+
+    private[this] var index = 0
+
+    def hasNext: Boolean = index < domList.length
+
+    def next(): T = {
+      val res = domList(index)
+      index += 1
+      res
+    }
+  }
 }
 
 /**
@@ -6308,10 +6335,9 @@ trait DOMList[T] extends js.Object {
  */
 @js.native
 @JSGlobal
-class NodeList extends DOMList[Node]
-
-@js.native
-trait NodeListOf[TNode <: Node] extends DOMList[TNode]
+class NodeList[+T <: Node] private[this] () extends DOMList[T] {
+  def item(index: Int): T = js.native
+}
 
 @js.native
 @JSGlobal
@@ -6832,7 +6858,9 @@ trait TextTrackCue extends EventTarget {
  * MDN
  */
 @js.native
-trait DOMTokenList extends DOMList[String] {
+@JSGlobal
+class DOMTokenList private[this] extends DOMList[String] {
+  def item(index: Int): String = js.native
 
   def contains(token: String): Boolean = js.native
 
@@ -7205,7 +7233,10 @@ trait ProgressEvent extends Event {
  * MDN
  */
 @js.native
-trait FileList extends DOMList[File]
+@JSGlobal
+class FileList private[this] () extends DOMList[File] {
+  def item(index: Int): File = js.native
+}
 
 /**
  * The File interface provides information about -- and access to the contents of --
@@ -7380,7 +7411,8 @@ trait AudioTrack extends js.Object {
 }
 
 @js.native
-trait TextTrackCueList extends DOMList[TextTrackCue] {
+@JSGlobal
+class TextTrackCueList private[this] () extends DOMList[TextTrackCue] {
   def getCueById(id: String): TextTrackCue = js.native
 }
 
@@ -7572,7 +7604,10 @@ trait WindowBase64 extends js.Object {
  * MDN
  */
 @js.native
-trait DOMStringList extends DOMList[String] {
+@JSGlobal
+class DOMStringList private[this] () extends DOMList[String] {
+  def item(index: Int): String = js.native
+
   def contains(str: String): Boolean = js.native
 }
 

src/main/scala/org/scalajs/dom/lib.scala

@@ -38,4 +38,7 @@ package object dom {
 
   @deprecated("use DOMRectList instead", "2.0.0")
   type ClientRectList = DOMRectList
+
+  @deprecated("use NodeList[T] instead", "2.0.0")
+  type NodeListOf[+T <: Node] = NodeList[T]
 }

src/main/scala/org/scalajs/dom/package.scala

@@ -81,7 +81,7 @@ object raw {
   type DOMException = dom.DOMException
   type DOMImplementation = dom.DOMImplementation
   lazy val DOMException: dom.DOMException.type = dom.DOMException
-  type DOMList[T] = dom.DOMList[T]
+  type DOMList[+T] = dom.DOMList[T]
   type DOMParser = dom.DOMParser
   type DOMRect = dom.DOMRect
   type DOMRectList = dom.DOMRectList
@@ -238,8 +238,8 @@ object raw {
   type NodeFilter = dom.NodeFilter
   lazy val NodeFilter: dom.NodeFilter.type = dom.NodeFilter
   type NodeIterator = dom.NodeIterator
-  type NodeList = dom.NodeList
-  type NodeListOf[TNode <: Node] = dom.NodeListOf[TNode]
+  type NodeList[+T <: Node] = dom.NodeList[T]
+  type NodeListOf[+T <: Node] = NodeList[T]
 
   type OfflineAudioContext = dom.OfflineAudioContext
   type OscillatorNode = dom.OscillatorNode