在 Javascript 中：您可以将 if/else 语句转换为开关吗？

Question

我试图将 Javascript 中的工作 If/Else 语句转换为 Switch 语句。 但是由于某种原因，我无法让 Switch 语句工作。 这可能/我有什么问题/语法错误吗？ 我已包含以下代码：有人可以为我澄清一下吗，谢谢。

工作 If/Else 语句：

function displayCityInfo() {
    var cd = document.getElementById("cityData").value;
    var h2 = document.getElementById("main");



    switch(cd){
      var spacing = "";
      case 1:

      for(i=0; i<cities.length; i++){
          spacing += "City of " + cities[i].city
          + ", latitude is " + cities[i].latitude + "<p>";
      }
      h2.innerHTML = "<h2>Results</h2>" + spacing;

        break;

      case 2:

      for(i=0; i<cities.length; i++){
          spacing += "City of " + cities[i].city
          + " population is " + cities[i].population + "<p>";
      }
      h2.innerHTML = "<h2>Results</h2>" + spacing;

      break;

      case 3:

      for(i=0; i<cities.length; i++){
          spacing += "City of " + cities[i].elevation
          + ", latitude is " + cities[i].elevation + "<p>";
      }
      h2.innerHTML = "<h2>Results</h2>" + spacing;

      break;

    }



}

Javascript Switch 语句不起作用：

function displayCityInfo() {
    var cd = document.getElementById("cityData").value;
    var h2 = document.getElementById("main");



    switch(cd){
      var spacing = "";
      case 1:

      for(i=0; i<cities.length; i++){
          spacing += "City of " + cities[i].city
          + ", latitude is " + cities[i].latitude + "<p>";
      }
      h2.innerHTML = "<h2>Results</h2>" + spacing;

        break;

      case 2:

      for(i=0; i<cities.length; i++){
          spacing += "City of " + cities[i].city
          + " population is " + cities[i].population + "<p>";
      }
      h2.innerHTML = "<h2>Results</h2>" + spacing;

      break;

      case 3:

      for(i=0; i<cities.length; i++){
          spacing += "City of " + cities[i].elevation
          + ", latitude is " + cities[i].elevation + "<p>";
      }
      h2.innerHTML = "<h2>Results</h2>" + spacing;

      break;

    }



}

Answer 1

启动 switch 后的 switch 语句，除了case或default 。 这意味着你不能放var spacing = ""; 低于switch(cd){ 。 在开关上方声明变量。

Answer 2

只需使用默认值，如下所示：

switch(x){
  case 1:
    //do stuff
  break;
  default:
    //do the stuff that you would do in the else block
  break;
}

注意：我不确定你为什么要在 if/else 上使用它，但你可以添加它，比如：

  case 1:
    //do stuff
  break;
  case 2:
    //do other stuff
  break;
  default:
    //do the stuff that you would do in the else block
  break;