scala.jsのサンプルアプリケーションで「暗黙のExecutionContextが見つかりません」というエラーが発生しました。ここで

Question

はハンズオンScala.jsのebookからの例です：コンパイルするとき

package webpage 

import org.scalajs.dom.ext.Ajax 

import scala.scalajs.js 
import scala.scalajs.js.annotation.JSExport 
import scalatags.JsDom.all._ 
import org.scalajs.dom 
import dom.html 

@JSExport 
object HelloWorld1 extends { 
    @JSExport 
    def main(target: html.Div) = { 

    lazy val box = input(
     `type`:="text", 
     placeholder:="Type here!" 
    ).render 

    lazy val output = div(
     height:="400px", 
     overflowY:="scroll" 
    ).render 

    box.onkeyup = (e: dom.Event) => { 
     output.innerHTML = "Loading..." 
     fetchWeather(box.value) 
    } 

    target.appendChild(
     div(
     h1("Weather Search"), 
     p(
      "Enter the name of a city to pull the ", 
      "latest weather data from api.openweathermap.com!" 
     ), 
     p(box), 
     hr, output, hr 
    ).render 
    ) 

    def fetchWeather(query: String) = { 
     val searchUrl = 
     "http://api.openweathermap.org/data/" + 
      "2.5/find?type=like&mode=json&q=" + 
      query 

     for{ 
     xhr <- Ajax.get(searchUrl) 
     if query == box.value 
     } js.JSON.parse(xhr.responseText).list match{ 
     case jsonlist: js.Array[js.Dynamic] => 
      output.innerHTML = "" 
      showResults(jsonlist, query) 
     case _ => 
      output.innerHTML = "No Results" 
     } 
    } 
    def showResults(jsonlist: js.Array[js.Dynamic], query: String) = { 
     for (json <- jsonlist) { 
     val name = json.name.toString 
     val country = json.sys.country.toString 
     val weather = json.weather.pop().main.toString 

     def celsius(kelvins: js.Dynamic) = { 
      kelvins.asInstanceOf[Double] - 273.15 
     }.toInt 

     val min = celsius(json.main.temp_min) 
     val max = celsius(json.main.temp_max) 
     val humid = json.main.humidity.toString 
     val (first, last) = name.splitAt(query.length) 
     output.appendChild(
      div(
      b(span(first, backgroundColor:="yellow"), last, ", ", country), 
      ul(
       li(b("Weather "), weather), 
       li(b("Temp "), min, " - ", max), 
       li(b("Humidity "), humid, "%") 
      ) 
     ).render 
     ) 
     } 
    } 
    } 
} 

はエラーを得た：ここが間違っていた

[info] Compiling 1 Scala source to /Users/kaiyin/personal_config_bin_files/workspace/workbench-example-app/target/scala-2.11/classes... 
[error] /Users/kaiyin/personal_config_bin_files/workspace/workbench-example-app/src/main/scala/HelloWorld1.scala:51: Cannot find an implicit ExecutionContext. You might pass 
[error] an (implicit ec: ExecutionContext) parameter to your method 
[error] or import scala.concurrent.ExecutionContext.Implicits.global. 
[error]   if query == box.value 
[error]    ^
[warn] /Users/kaiyin/personal_config_bin_files/workspace/workbench-example-app/src/main/scala/HelloWorld1.scala:53: non-variable type argument scala.scalajs.js.Dynamic in type pattern scala.scalajs.js.Array[scala.scalajs.js.Dynamic] is unchecked since it is eliminated by erasure 
[warn]   case jsonlist: js.Array[js.Dynamic] => 
[warn]       ^
[warn] one warning found 
[error] one error found 
[info] workbench: Checking example-fastopt.js 
[info] workbench: Checking webpage-fastopt.js 
[error] (compile:compile) Compilation failed 
[error] Total time: 0 s, completed 7 sept. 2015 12:51:38 
78. Waiting for source changes... (press enter to interrupt) 

何？

Answer 1

エラーが示すように、次のインポートを追加します。

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