Find adjacent entries for a javascript Map? -

given

var mymap = new map() mymap.set("alpha", "first") mymap.set("beta", "second") mymap.set("charlie", "third") mymap.set("delta", "fourth") mymap.set("echo", "fifth") mymap.set("foxtrot", "sixth") 

starting given key...

mymap.get("charlie") //=> "third" 

... how values surrounding keys?

// pseudo code mymap.get("charlie").prev() //=> "second" mymap.get("charlie").next() //=> "fourth" 

ideally, i'd while iterating on mymap:

var valuesicareabout = [];  mymap.foreach(function(value, key, map) {   valuesicareabout.push({     callsign: key,     callvalue: value,     nextcallvalue: map.get(key).next(), // pseudo code     prevcallvalue: map.get(key).prev()  // pseudo code   }); }); 

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in actual use case, keys of map dom nodes, , need siblings in order calculate position offsets. expected prev value first node in map null , next value last node in map null.

that make sense?

how iterating on keys of map array?

var keys = array.from(map.keys()); keys.foreach(function(key, i, keys) {     var current = map.get(key);     var previous = map.get(keys[i-1]);     var next = map.get(keys[i+1]);     // ... }); 

(obviously have account first , last element here)

if internal code, think extending existing map class own foreach implementation passes previous , next value callback.