Example view map function

priority.js

var priorities = [
  "!urgent",
  null,
  "!soon",
  "!normal",
  "!backlog",
  "!wishlist",
]

function getPriorityOrder(task) {
  var taskPriorityKey = -1
  var tagIds = task.tagIds
  if(tagIds){
    for(var tagPos = tagIds.length; tagPos-->0;){
      var tagId = tagIds[tagPos]
      if(tagId.charAt(0)==="!"){
        var priorityKey = priorities.indexOf(tagId)
        if(priorityKey !== -1){
          if((taskPriorityKey!== -1) && (taskPriorityKey <= priorityKey)){
            continue //keep the more urgent priority
          }
          else{
            taskPriorityKey = priorityKey
          }
        }
      }
    }
  }
  if(taskPriorityKey !== -1){
    return taskPriorityKey
  }
  else{
    return priorities.indexOf(null)
  }
}

function getKey(doc) {
  if(doc.type && doc.type === "task"){
    emit(getPriorityOrder(doc))
  }
}

getKey