在JavaScript

Question

我有以下代码。出于某种原因，我不想执行的案例陈述（第二个案例＆＃39; 2＆＃39;）除了正确的案例之外还要执行（Case＆＃39; 4＆＃39;）。在线阅读后，大多数人都可以通过添加＆＃34; break＆＃34;来解决类似的问题。声明。但它并不适合我。请指教。以下输出来自我的浏览器

＆＃13;

＆＃13;

var chk = '4'

switch (chk) {
  case '4':
    var locations = [
      ["936001_STURGEON_BAY_MEYER", 44.8358, -87.3305, "LRA", 1],
      ["936087_SHADOW_LAKE", 45.2183, -88.5981, "LRA", 2],
      ["936136_PIG", 44.5925, -88.0808, "OMS", 3],
      ["936136_PIG", 44.5925, -88.0808, "OMS", 4]
    ];

    var map = new google.maps.Map(document.getElementById('map'), {
      zoom: 15,
      center: new google.maps.LatLng(locations[0][1], locations[0][2]),
      mapTypeId: google.maps.MapTypeId.ROADMAP
    });

    var infowindow = new google.maps.InfoWindow({
      maxWidth: 400000
    });
    var locations_all_cells1 = locations;
    var marker, i;

    for (i = 0; i < locations_all_cells1.length; i++) {
      var type1 = locations_all_cells1[i][3];

      switch (type1) {
        case "OMS":
          marker1 = new google.maps.Marker({
            position: new google.maps.LatLng(locations_all_cells1[i][1], locations_all_cells1[i][2]),
            map: map,
            icon: 'http://maps.google.com/mapfiles/ms/icons/green-dot.png'
          });
          google.maps.event.addListener(marker1, 'click', (function(marker1, i) {
            return function() {
              infowindow.setContent(locations_all_cells1[i][0]);
              infowindow.open(map, marker1);
            }
          })(marker1, i));
          break;

        case "LRA":
          marker2 = new google.maps.Marker({
            position: new google.maps.LatLng(locations_all_cells1[i][1], locations_all_cells1[i][2]),
            map: map,
            icon: 'http://maps.google.com/mapfiles/ms/icons/red-dot.png'
          });
          google.maps.event.addListener(marker2, 'click', (function(marker2, i) {
            return function() {
              infowindow.setContent(locations_all_cells1[i][0]);
              infowindow.open(map, marker2);
            }
          })(marker2, i));
          break;

        case "UPSAVE":
          marker3 = new google.maps.Marker({
            position: new google.maps.LatLng(locations_all_cells1[i][1], locations_all_cells1[i][2]),
            map: map,
            icon: 'http://maps.google.com/mapfiles/ms/icons/yellow-dot.png'
          });
          google.maps.event.addListener(marker3, 'click', (function(marker3, i) {
            return function() {
              infowindow.setContent(locations_all_cells1[i][0]);
              infowindow.open(map, marker3);
            }
          })(marker3, i));
      }
    }
    break;

  case '2':
    var locations = [
      ["936001_STURGEON_BAY_MEYER", 44.8358, -87.3305, "LRA", 1],
      ["936087_SHADOW_LAKE", 45.2183, -88.5981, "LRA", 2],
      ["936136_PIG", 44.5925, -88.0808, "OMS", 3],
      ["936136_PIG", 44.5925, -88.0808, "OMS", 4]
    ];

    var map = new google.maps.Map(document.getElementById('map'), {
      zoom: 15,
      center: new google.maps.LatLng(locations[0][1], locations[0][2]),
      mapTypeId: google.maps.MapTypeId.ROADMAP
    });

    var infowindow = new google.maps.InfoWindow({
      maxWidth: 400000
    });
    var locations_all_cells = ;
    var marker, i;

    for (i = 0; i < locations_all_cells.length; i++) {
      var type1 = locations_all_cells[i][3];
    }
    break;
    
  default:
    text = "Looking forward to the Weekend";
}
console.log(text);

＆＃13;

＆＃13;

＆＃13;

错误信息

Answer 1

来自MDN Docs for switch：

  

switch语句首先计算其表达式。然后，它查找第一个case子句，其表达式的计算结果与输入表达式（使用严格比较，===）的结果相同，并将控制转移到该子句，执行关联的语句。

switch执行严格检查，与您的'4'（字符串）和4（数字）不匹配。所以你需要改变你的代码，如：

var chk = '4';

<强>更新

如果您的浏览器确实正确加载了它，例如chk = '4'，那么它应该可以正常运行。见这里：

var chk = '4';
// Added this for checking.
var type1 = 'OMS';

switch (chk) {
  case '4':
    switch (type1) {
      case "OMS":
        text = "4 - OMS";
        break;
      case "LRA":
        text = "4 - LRA";
        break;
      case "UPSAVE":
        text = "4 - UPSAVE";
    }
    break;
  case '2':
    // ####Do some Stuff here##
    break;
  default:
    text = "Looking forward to the Weekend";
}
console.log(text);

Answer 2

我终于在朋友的帮助下解决了我的问题。事实证明，Javascript不喜欢未初始化的case语句中的变量。在其中一个case语句中，我使用的是一个变量，我之前根据某些逻辑为其分配了一个值。尽管此案例陈述未被评估为＆＃34; true＆＃34;我的程序抛出错误。

例如，在下面的代码中，如果b为空/空，则程序n和m会出错，即使m是＆＃34; false＆＃34;：

switch(expression) {
case n:
    break;
case m:
    Var a=b;
    break;
default:
    default code block
}