a minimal lru structure for js

lru.js

/**
 * Create dead-simple LRU structure.
 * @param {Number} size maximum number of items to be stored.
 * @param {Object} [init] initial contents.
 * @return {Object} the LRU object
 */
function LRU( size, init ) {
  var items = init || Object.create( null );
  var keys = Object.keys( items );

  function pop( key ) {
    var value = items[ key ];
    var index = keys.indexOf( key );

    delete items[ key ];

    if( index >= 0 ) {
      keys.splice( index, 1 );
    }
    return value;
  }

  function push( key, value ) {
    keys.push( key );
    items[ key ] = value;

    if( keys.length > size ) {
      delete items[ keys.shift() ];
    }
  }

  function use( key ) {
    var index = keys.indexOf( key );

    if( index >= 0 ) {
      keys.splice( index, 1 );
      keys.push( index );
    }
  }

  return {
    has: function has( key ) {
      return key in items;
    },
    get: function get( key ) {
      use( key );
      return items[ key ];
    },
    set: function set( key, value ) {
      pop( key );
      push( key, value );
      return value;
    },
    push: push,
    pop: pop,
    clear: function clear() {
      items = {};
      keys = [];
    }
  };
}