如何使用jQuery从嵌套的JSON字符串中获取值？

我有以下JSON字符串，由输出：

{
       "event":"build",
       "tab":"map",
       "selection":{
          "tier":{
             "id":1,
             "parentId":0,
             "label":"ca",
             "level":100,
             "hashKey":"object:5"
          },
          "group":{
             "id":2,
             "parentId":1448818,
             "label":"com",
             "spatialLevelId":203,
             "hashKey":"object:11"
          },
          "area":{
             "id":3,
             "parentId":1449705,
             "label":"cam",
             "level":303,
             "hashKey":"object:14"
          },
          "indicators":[

          ]
       }
    }

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如何仅从所有3个部分（层、组、区域）获取级别并将其放入变量中？

您可以按如下方式检索值

function handler(message) {
     var tierSpatialLevelId = message.selection.tier.spatialLevelId; 
     var groupSpatialLevelId = message.selection.group.spatialLevelId;
     var areaSpatialLevelId = message.selection.area.spatialLevelId; 
}