A basic implementation of a multi-field map, where each mapping consists of a number of keyed properties, and a record may be retrieved based on any one of those fields. Works well for scenarios where you would reach for a Map, but want to be able to retrieve a key from its corresponding value; also multi-dimensional mappings, where you want to …

multiMap.js

function multiMap( keys ){
  const lists = {}

  keys.forEach( key => lists[ key ] = [] )
  
  return {
    set( entry ){
      let index = lists[ keys[ 0 ] ].indexOf( entry[ keys[ 0 ] ] )

      if( index < 0 ) index = lists[ key[ 0 ] ].length

      keys.map( key => lists[ key ][ index ] = entry[ key ] )
    }

    get( key, value ){
      const record = Object.create( null )
      const index = lists[ key ].getIndexOf( value )

      keys.forEach( key => record[ key ] = list[ key ][ index ] )

      return record
    }
  }
}