Improved the repl binding

src/main/scala/io/scalajs/nodejs/Process.scala

@@ -53,7 +53,7 @@ trait Process extends IEventEmitter {
   /**
     * An object containing the user environment.
     */
-  def env: js.Dictionary[String] = js.native
+  def env: Environment = js.native
 
   /**
     * This is the set of Node.js-specific command line options from the executable that started the process.

src/main/scala/io/scalajs/nodejs/package.scala

@@ -18,6 +18,8 @@ package object nodejs {
     */
   type FileDescriptor = Integer
 
+  type Environment = js.Dictionary[String]
+
   /////////////////////////////////////////////////////////////////////////////////
   //      Built-in Properties
   /////////////////////////////////////////////////////////////////////////////////

src/main/scala/io/scalajs/nodejs/repl/REPL.scala

@@ -18,7 +18,7 @@ import scala.scalajs.js.|
 trait REPL extends IEventEmitter {
   var REPL_MODE_SLOPPY: String = js.native
   var REPL_MODE_STRICT: String = js.native
-  var REPL_MODE_MAGIC: String  = js.native
+  var REPL_MODE_MAGIC: String = js.native
 
   /**
     * @example repl.start([options])

src/main/scala/io/scalajs/nodejs/repl/REPLServer.scala

@@ -15,30 +15,34 @@ trait REPLServer extends IEventEmitter with Interface {
   /**
     * The REPL's context
     */
-  // TODO find document for this property
-  val context: js.Dynamic = js.native
+  val context: REPLContext = js.native
 
   /**
-    * Makes a command available in the REPL. The command is invoked by typing a . followed by the keyword.
-    * The cmd is an object with the following values:
+    * The replServer.defineCommand() method is used to add new .-prefixed commands to the REPL instance.
+    * Such commands are invoked by typing a period (.) followed by the keyword. The cmd is either a Function
+    * or an object with the following properties:
     * <ul>
-    * <li>help - help text to be displayed when .help is entered (Optional).</li>
-    * <li>action - a function to execute, potentially taking in a string argument, when the command is invoked,
-    * bound to the REPLServer instance (Required).</li>
+    * <li>help (string) Help text to be displayed when .help is entered (Optional).</li>
+    * <li>action (Function) The function to execute, optionally accepting a single string argument.</li>
     * </ul>
-    * If a function is provided instead of an object for cmd, it is treated as the action.
-    * @example replServer.defineCommand(keyword, cmd)
+    * @param keyword The command keyword (without a leading . character).
+    * @param cmd     The function to invoke when the command is processed.
     */
-  def defineCommand(keyword: String, cmd: js.Any): Unit = js.native
+  def defineCommand(keyword: String, cmd: js.Function0[Any]): Unit = js.native
 
   /**
-    * Like readline.prompt except also adding indents with ellipses when inside blocks. The preserveCursor argument
-    * is passed to readline.prompt. This is used primarily with defineCommand. It's also used internally to render
-    * each prompt line.
-    * @example replServer.displayPrompt([preserveCursor])
-    * @see [[prompt()]]
+    * The replServer.displayPrompt() method readies the REPL instance for input from the user, printing the
+    * configured prompt to a new line in the output and resuming the input to accept new input.
+    *
+    * When multi-line input is being entered, an ellipsis is printed rather than the 'prompt'.
+    * *
+    * When preserveCursor is true, the cursor placement will not be reset to 0.
+    *
+    * The replServer.displayPrompt method is primarily intended to be called from within the action function
+    * for commands registered using the replServer.defineCommand() method.
+    * @param preserveCursor indicates whether to preserver the cursor (position?)
     */
-  def displayPrompt(preserveCursor: Boolean): Unit = js.native
+  def displayPrompt(preserveCursor: Boolean = js.native): Unit = js.native
 
   /**
     * Like readline.prompt except also adding indents with ellipses when inside blocks. The preserveCursor argument

src/main/scala/io/scalajs/nodejs/repl/package.scala

@@ -0,0 +1,88 @@
+package io.scalajs.nodejs
+
+import scala.scalajs.js
+
+/**
+  * repl package object
+  * @author [email protected]
+  */
+package object repl {
+
+  type REPLContext = js.Dynamic
+
+  /**
+    * REPL Server events
+    * @param server the given [[REPLServer instance]]
+    */
+  final implicit class REPLServerEvents(val server: REPLServer) extends AnyVal {
+
+    @inline
+    def contextAs[T]: T = server.context.asInstanceOf[T]
+
+    /**
+      * The 'exit' event is emitted when the REPL is exited either by receiving the .exit command as input,
+      * the user pressing CTRL-C twice to signal SIGINT, or by pressing CTRL-D to signal 'end' on the input stream.
+      * The listener callback is invoked without any arguments.
+      * @param listener The listener callback
+      */
+    @inline
+    def onExit(listener: () => Any): server.type = server.on("exit", listener)
+
+    /**
+      * The 'reset' event is emitted when the REPL's context is reset. This occurs whenever the .clear command
+      * is received as input unless the REPL is using the default evaluator and the repl.REPLServer instance
+      * was created with the useGlobal option set to true. The listener callback will be called with a reference
+      * to the context object as the only argument.
+      * @param listener The listener callback
+      */
+    @inline
+    def onReset(listener: REPLContext => Any): server.type = server.on("reset", listener)
+
+  }
+
+  /**
+    * Various behaviors of the Node.js REPL can be customized using the following environment variables:
+    * <ul>
+    * <li>NODE_REPL_HISTORY</li>
+    * <li>NODE_REPL_HISTORY_SIZE</li>
+    * <li>NODE_REPL_MODE</li>
+    * </ul>
+    */
+  final implicit class EnvironmentVariableOptions(val env: Environment) extends AnyVal {
+
+    /**
+      * When a valid path is given, persistent REPL history will be saved to the specified file rather
+      * than .node_repl_history in the user's home directory. Setting this value to "" will disable persistent
+      * REPL history. Whitespace will be trimmed from the value.
+      */
+    @inline
+    def NODE_REPL_HISTORY: Option[String] = env.get("NODE_REPL_HISTORY")
+
+    /**
+      * Previously in Node.js/io.js v2.x, REPL history was controlled by using a NODE_REPL_HISTORY_FILE environment
+      * variable, and the history was saved in JSON format. This variable has now been deprecated, and the old
+      * JSON REPL history file will be automatically converted to a simplified plain text format. This new file
+      * will be saved to either the user's home directory, or a directory defined by the NODE_REPL_HISTORY variable,
+      * as documented in the Environment Variable Options.
+      */
+    @inline
+    @deprecated("Use NODE_REPL_HISTORY instead.", since = "3.0.0")
+    def NODE_REPL_HISTORY_FILE: Option[String] = env.get("NODE_REPL_HISTORY_FILE")
+
+    /**
+      * Defaults to 1000. Controls how many lines of history will be persisted if history is available.
+      * Must be a positive number.
+      */
+    @inline
+    def NODE_REPL_HISTORY_SIZE: Option[Int] = env.get("NODE_REPL_HISTORY_SIZE").map(_.toInt)
+
+    /**
+      * May be any of sloppy, strict, or magic. Defaults to magic, which will automatically run "strict mode only"
+      * statements in strict mode.
+      */
+    @inline
+    def NODE_REPL_MODE: Option[String] = env.get("NODE_REPL_MODE")
+
+  }
+
+}