a cache library
$ npm install lcache
or
$ yarn add lcache
import LCache from 'lcache';
var lcache = new LCache(100);
or
const LCache = require('lcache').default;
lcache.put('key', value);
if the size is over the limit, return the head
lcache.get('key');
return undefined if the key is not exists
lcache.shift('key')
remove the specified entry or the head if key is undefined