不可变的JS OrderedMap:在给定的Key之后插入一个新条目

问题描述

我有一个不可变的OrderedMap，如下所示:

I have an Immutable OrderedMap as follows:

pairs: Immutable.OrderedMap({"Key1":"Value1","Key2":"Value2","Key4":"Value4"})

我需要在["Key2":"Value2"]之后动态插入["Key3":"Value3"].

I need to insert ["Key3":"Value3"] after ["Key2":"Value2"] dynamically.

我以为

pairs.MergeIn(['Key2'],OrderedMap({"Key3":"Value3"}))

将达到目的，但不起作用.

will serve the purpose but not working.

我尝试了

const newPairs=Immutable.OrderedMap();
newPairs.forEach(function(value,key,map)){
   if(key=="Key4")
     newPairs.set('Key3','Value3')
   newPairs.set(key,value')
});

但是我知道这是一个愚蠢的代码，因为newPairs是不可变的，并且newPairs将仍然为空，因此它无法正常工作.那么，OrderedMap.addBefore(Key，key，value)有什么不可变的方法吗?

But I know it's a stupid code which won't work as newPairs is immutable and newPairs will be still empty.So is there any Immutable way of OrderedMap.addBefore(Key,key,value)?

推荐答案

OrderedMap 保留插入顺序，因此您只需要创建一个新的 OrderedMap 即可，插入正确的位置:

OrderedMap preserves the order of insertions, so you just need to create a new OrderedMap where the value is inserted at the correct place:

function printMap(map) {
  map.entrySeq().map(([key, val]) => console.log(key, val)).toJS()
}

function insertBefore(map, index, key, val) {
  return Immutable.OrderedMap().withMutations(r => {
    for ([k, v] of map.entries()) {
      if (index === k) {
        r.set(key, val)
      }
      r.set(k, v)
    }
 });
}


const o1 = Immutable.OrderedMap().set('key1', 'val1').set('key2', 'val2');
printMap(o1)

console.log('now insert before');
printMap(insertBefore(o1, 'key2', 'key1.1', 'val1.1'))

<script src="https://cdnjs.cloudflare.com/ajax/libs/immutable/3.8.1/immutable.min.js"></script>

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