直接上代码
//交集
let intersect = a.filter(v => b.includes(v));
//差集
let minus = a.filter(v => !b.includes(v));
//补集
let complement = a.filter(v => !b.includes(v)).concat(b.filter(v => !a.includes(v)))
//并集
let unionSet = a.concat(b.filter(v => !a.includes(v)));
Chongyang Festival(重阳节), also called the Double Ninth Festival(九九节), falls on the ninth day of the ninth lunar month(阴历九月初九). It is named as Chongyang Festival because according to the Chinese astrology(中国古代占星术), nine is a 'Yang' character meaning masculine or positive and 'Chong' in Chinese means double. As both the month and the day are nine, it got this name. Double Ninth may have originated as a day to drive away danger.
In China, nine has the similar pronunciation(发音相似) with the word meaning 'forever', symbolizing longevity(象征长寿). Therefore, the Chinese government set the day as the Seniors' Day(老人节).
重阳节名字知多少？
- Double Ninth Festival（重阳节）；
- Seniors' Day （老人节）；
- Height Ascending Festival（登高节）；
- Chrysanthemum Festival（菊花节）。
重阳节的庆祝方式：
Showing respect to the seniors(尊敬长辈)
Climbing mountains（登山）
Eating Chongyang cakes（吃重阳饼）
Drinking chrysanthemum wine（喝菊花酒）
Enjoying chrysanthemum and sticking chrysanthemum,（赏菊和插菊花）
有关重阳节的传说
During the East Han Dynasty, there was a devil of the plague in the Ruhe River. As long as it showed up, people got sick and even died. People living around the Ruhe River suffered a lot from the disease ravaged by demons.
相传在东汉时期，汝河有个瘟魔，只要它一出现，家家就有人病倒，天天有人丧命。周边百姓受尽了瘟魔的蹂躏。
There lived a man named Huan Jing. His parents died from the plague and he almost died. After he recovered, Huan Jing decided to learn the magic arts and killed the devil of the plague. Huan Jing heard that there an immortal lived in the eastern area. He took a long journey and finally found the immortal. The immortal was moved by his behavior and taught Huan Jing how to kill the devil of the plague.
有一位叫桓景的一个年轻人，一场瘟疫夺走了青年桓景的父母，他自己也因病差点毕命。病愈之后，他决心出去访仙学艺，为民除掉瘟魔。桓景四处访师寻道，终于打听到在东方有一座最古老的山，山上有一个法力无边的仙长，桓景不畏艰险和路途的遥远，终于找到了那个有着神奇法力的仙长，仙长为他的精神所感动并教给他降妖剑术。
One day, the immortal told Huan Jing that the devil of the plague would show up again on the ninth day of the ninth month, and he asked Huan Jing to go back to kill it. When Huan Jing went back, he asked the whole family to go to a mountain and sent everyone a Zhuyu leaf and a glass of chrysanthemum wine. When the devil of the plague emerged from the water, it got dizzy from the scent of the Zhuyu and the chrysanthemum. At that time, Huan Jing took the sword and killed the devil of the plague. Since then, climbing mountains has become a custom on the Double Ninth Festival.
一天，仙长把桓景叫到跟前说：“明天是九月初九，瘟魔又要出来作恶，你本领已经学成，应该回去为民除害了”。桓景回到家乡，把乡亲们领到了附近的一座山上，发给每人一片茱萸叶，一盅菊花酒，做好了降魔的准备。中午时分，随着几声怪叫，瘟魔冲出汝河，但是瘟魔刚扑到山下，突然闻到阵阵茱萸奇香和菊花酒气，便戛然止步，脸色突变，这时桓景手持降妖宝剑追下山来，几个回合就把温魔刺死剑下，从此九月初九登高避疫的风俗年复一年地流传下来。
九月九日憶山東兄弟
（唐代诗人 王维）
獨在異鄉為異客，
每逢佳節倍思親。
遙知兄弟登高處，
遍插茱萸少一人。
Double Ninth, Remembering my Shandong Brothers
By the Tang Dynasty poet Wang Wei:
As a lonely stranger in a foreign land,
At every holiday my homesickness increases.
Far away, I know my brothers have reached the peak;
They are wearing the zhuyu, but one is not present.