Given an absolute path for a file (Unix-style), simplify it.

Simplify-Path.js

/**
 * @param {string} path
 * @return {string}
 */
const PATH_START = 0
const PATH_END = 1
const PATH_READ = 2
const PATH_CURRENT = 3
const PATH_PARENT = 4

var simplifyPath = function(path) {
    var aim = [],len = path.length,index = 0,char,state = PATH_START,
        tmp = ''        

    while(index < len){
        char = path[index]
        index += 1
        switch (char) {
            case '/':
                //路径开始
                if(state === PATH_READ){
                    if(tmp){
                        aim.push(tmp)
                        tmp = ''
                    }
                }else if(state === PATH_END){ // 已经到结束符号了则直接跳过,xx//xx//
                    continue
                }
                state = PATH_END
                break;
            case '.':
                if(state === PATH_END){//进入当前目录 .
                    state = PATH_CURRENT
                }else if(state === PATH_CURRENT){ // 返回上一级 ../
                    state = PATH_PARENT
                    aim.pop()
                }else if(state === PATH_PARENT){
                    state = PATH_CURRENT
                }else if(state === PATH_READ){
                    tmp += char
                }
                break;
            default:
                tmp += char
                state = PATH_READ
                break;
        }   
    }
    if(state !== PATH_END){
        aim.push(tmp)
    }

    return '/' + aim.join('/')
};