Practicing System Design in JavaScript: Cache System and the Shortest Path for Graph

Introduction
Data structure is one of unavoidable challenges when applying the software engineer role. I studied basic data structures and wrote down an article in JavaScript before.

However, it’s hard to apply data structures to design a system or solve the real problem.

The target of article is for recording common problems with data structures. I choose two interesting problems from Cracking the coding Interview and turn the solutions to JavaScript. We will use hash table, linked list, list(array) to solve these questions.

Please Design a Cache for a Single System?
How to Find the Shortest Search Path between Two People?

Please Design a Cache for a Single System?
Requirements
Design a cache system with the following properties.