添加元素
let list = new Set();
list.add(1)
list.add(2).add(3).add(3) // 2只被添加了一次
console.log(list);
删除元素
let list=new Set([1,20,30,40])
list.delete(30) //删除值为30的元素，这里的30并非下标
console.log(list);
判断某元素是否存在
let list=new Set([1,2,3,4])
console.log(list.has(2));
清除所有元素
let list=new Set([1,2,3,4])
list.clear()
console.log(list);
遍历 keys()
let list2=new Set(['a','b','c'])
for(let key of list2.keys()){
console.log(key)//a,b,c
}
遍历 values()
let list=new Set(['a','b','c'])
for(let value of list.values()){
console.log(value)//a,b,c
}
遍历 entries()
let list=new Set(['4','5','hello'])
for (let item of list.entries()) {
console.log(item);
} // ['4','4'] ['5','5'] ['hello','hello']
遍历 forEach()
let list=new Set(['4','5','hello'])
list.forEach((value, key) => console.log(key + ' : ' + value)) // 4:4 5:5 hello:hello
用于数组去重
let arr = [3, 5, 2, 2, 5, 5];
let setArr = new Set(arr) // 返回set数据结构 Set(3) {3, 5, 2}
console.log(setArr);
//方法一 es6的...解构
let unique1 = [...setArr ]; //去重转数组后 [3,5,2]
console.log(unique1);
//方法二 Array.from()解析类数组为数组
let unique2 = Array.from(setArr ) //去重转数组后 [3,5,2]
console.log(unique2);
用于字符串去重
let str = "352255";
let unique = [...new Set(str)].join(""); // 352
console.log(unique);
实现并集、交集、和差集
并集
let union = new Set([...a, ...b]);
// Set {1, 2, 3, 4}
console.log(union);
交集
let intersect = new Set([...a].filter(x => b.has(x)));
// set {2, 3}
console.log(intersect);
（a 相对于 b 的）差集
let difference = new Set([...a].filter(x => !b.has(x)));
// Set {1}
console.log(difference);
数组中取最小
console.log(Math.min.apply(Math,[1,2,3,54,7,45,84]));
数组中取最大
console.log(Math.max.apply(Math,[1,2,3,54,7,45,84]));
