JavaScriptのPromiseとScalaのPromiseは別物で、むしろScalaのFutureが似てる話 ref: http://qiita.com/sifue/items/4a003ce1edd519076546

file0.js

function doubleUp(value) {
    return value * 2;
}
function increment(value) {
    return value + 1;
}
function output(value) {
    console.log(value);
}
var promise = new Promise(function (resolve) {
        resolve(1);
});
promise
    .then(increment)
    .then(doubleUp)
    .then(output) // 4が出力される
    .catch(function(error){
        console.error(error);
    });

file1.scala

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent._

object MainFuture extends App {
  def double(value: Int): Int = value * 2
  def increment(value: Int): Int = value + 1
  def output(value: Int): Unit  = Console.println(value)

  val future = Future {1}
  (for {
    i1 <- future
    i2 <- Future {increment(i1)}
    i3 <- Future {double(i2)}
  } yield output(i3)) // 4が出力される
    .onFailure { case t: Throwable =>
      Console.println(t.getMessage)
    }

  Thread.sleep(1000)
}

file2.scala

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent._

object MainPromise extends App {
  def output(value: Int): Unit  = Console.println(value)

  val promise = Promise[Int]
  Future {
    promise.trySuccess(0)
  }
  Future {
    Thread.sleep(100)
    promise.trySuccess(1)
  }
  promise.future.map(output) // 先に終了する0が出力される

  Thread.sleep(1000)
}