javascript 闭包应用：缓存

import {readFileSync, readdirSync} from 'fs';

var readContent = (function(){
  let contentCache = {};

  return (bookName)=>{
    let content = contentCache[bookName];
    if (!content){
      content = readFileSync(bookName+".txt", "utf8");
      contentCache[bookName] = content;
    }else{
      // console.info(content);
    }
    return content;
  };
})();